docs(glossy): Add and modify first-use behaviour

Add a mode, two modifiers and change the default usage behaviour of some
modes. This documents the glossy 'API' when using terms with respect to
the usage counter.

Important!
At the moment, this is a description of the intended endresult
(documentation driven development). Next commits will bring the code in
accordance with this desired result.

glossy/README.md

@@ -224,15 +224,15 @@ first use (`usage counter == 0`), 'both' forms are printed. On subsequent usage
 (`usage counter > 0`) the 'short' form is printed.
 
 Not all occurrences of a term are counted towards its usage, this depends on
-the mode of the term.
+the mode of the term. Furthermore, this can be manually controlled by modifiers.
-They are documented in the [reference tables](#reference-for-using-glossary-terms).
+Both are documented in the [reference tables](#reference-for-using-glossary-terms).
 
 This control over the usage counter is practical, for example, when you want to
 use a term in a heading or a caption.
 In that case, your term might end up in an `outline()` at the top of
 your document. Normally you don't want that to count as a term's first real use.
 Normally you want that to happen in the body of your document. So, by using
-the appropriate mode in such situations, you can not only specify
+the appropriate mode and modifiers in such situations, you can not only specify
 exactly how you want your term to appear, but also control whether it counts
 as a "first use".
 
@@ -241,6 +241,7 @@ as a "first use".
 A reference about
 - the different 'modes' and how they determine which information is printed about a term
 - the impact of modes on the [usage counter and ensuing first use behaviour](#first-use-logic)
+- how modifiers can change the behaviour with respect to the usage counter
 - how modifiers impact the presentation of the information printed
 
 A glossary term can display different types of information, which is determined
@@ -249,16 +250,17 @@ by the 'mode' in which it is printed. These modes are all mutually exclusive.
 | Mode          | Utilization         | Default first use behaviour | Description |
 | ------------- | ------------------- | --------------------------- | ----------- |
 | `auto`        | `@term`             | use       | The default mode when no 'mode' modifier or supplement is specified. The form depends on the first use counter. |
-| `both`        | `:both`             | no-use    | Shows both forms of the term, by default ([see `format-term`](#customizing-term-display)) like "Long Form (Short Form)". |
+| `both`        | `:both`             | use       | Shows both forms of the term, by default ([see `format-term`](#customizing-term-display)) like "Long Form (Short Form)". |
 | `short`       | `:short`            | no-use    | Shows only short form.        |
 | `long`        | `:long`             | no-use    | Shows only long form.         |
 | `description` | `:def` <br> `:desc` | no-use    | Shows the description (None of the modifiers apply here & no link is created towards the glossary). |
-| `supplement`  | `[content]`         | use       | Shows the content given by [the supplement](#overriding-term-text). |
+| `supplement`  | `[content]`         | no-use    | Shows the content given by [the supplement](#overriding-term-text). |
+| `reset`       | `:reset`            | reset usage counter to 0 | Don't output any content & don't link to the glossary. Typical usage would be after an abstract or even before the start of each chapter, maybe in an injected rule. (This could be made a modifier like `:use` or `:nouse`, but would mostly be utilized as `@term:reset:noindex[]` anyways, thus this is a mode. Write `@term@term:reset` to utilize it as a modifier.) |
 
-Minor modifications to how these different types of information are printed or
+Minor modifications to how these different types of information are printed,
-linked, are controlled by the 'modifiers'.
+linked or counted towards the usage counter, are controlled by the 'modifiers'.
-They do not influence the default first use behaviour of the mode (except `noindex`).
+They do not influence the default first use behaviour of the mode (unless
-Moreover, they neatly compose together
+explicitely created for this purpose). Moreover, they neatly compose together
 and with most modes (some exceptions exists, but will print a clear error -
 report a bug if not).
 
@@ -266,8 +268,10 @@ report a bug if not).
 | ------------------------------ | ---------------------------------------------------------------------- |
 | `:cap`                         | Capitalizes the term                                                   |
 | `:pl`                          | Uses the plural form                                                   |
-| `:noref` <br> `:noindex`       | Don't show the term in the glossary (i.e. no page will be linked - a link from the term towards the glossary is always provided.) AND don't count towards the usage counter. |
+| `:noref` <br> `:noindex`       | Don't show the term in the glossary (i.e. no page will be linked - a link from the term towards the glossary is always provided.). |
 | `:a`<br>`a:`<br>`:an`<br>`an:` | Include the article (`an` is just an alias of `a`, they're equivalent) |
+| `:use` <br> `:spend`           | After this occurrence, the term is 'used', i.e. the usage counter is increased by 1. Write `@term:use:noindex[]` to uniquely control the usage counter without output. |
+| `:nouse` <br> `:nospend`       | After this occurrence, the usage counter remains exactly as the same as before. As if the term is transparent with respect to the usage counter. |
 
 ### Generating the Glossary