Subtree memorization / reactive templates (#488)

This commit adds subtree memoization to Dioxus.

Subtree memoization is basically a compile-time step that drastically 
reduces the amount of work the diffing engine needs to do at runtime by
extracting non-changing nodes out into a static "template." Templates 
are then understood by the various renderers in the ecosystem as a 
faster way of rendering the same items. 

For example, in the web, templates are simply a set of DOM Nodes created 
once and then cloned later. This is the same pattern frameworks like Lithtml
and SolidJS use to achieve near-perfect performance. 

Subtree memoization adds an additional level of complexity to Dioxus. The RSX
macro needs to be much smarter to identify changing/nonchanging nodes and
generate a mapping between the Template and its runtime counterparts.

This commit represents a working starter point for this work, adding support 
for templates for the web, desktop, liveview, ssr, and native-core renderers.
In the future we will try to shrink code generation, generally improve 
performance, and simplify our implementation.

docs/guide/src/en/roadmap.md

@@ -50,7 +50,7 @@ Generally, here's the status of each platform:
 | 1st class global state    | ✅      | redux/recoil/mobx on top of context                                  |
 | Runs natively             | ✅      | runs as a portable binary w/o a runtime (Node)                       |
 | Subtree Memoization       | ✅      | skip diffing static element subtrees                                 |
-| High-efficiency templates | 🛠      | rsx! calls are translated to templates on the DOM's side             |
+| High-efficiency templates | ✅      | rsx! calls are translated to templates on the DOM's side             |
 | Compile-time correct      | ✅      | Throw errors on invalid template layouts                             |
 | Heuristic Engine          | ✅      | track component memory usage to minimize future allocations          |
 | Fine-grained reactivity   | 👀      | Skip diffing for fine-grain updates                                  |
@@ -66,7 +66,7 @@ These Features are planned for the future of Dioxus:
 ### Core
 - [x] Release of Dioxus Core
 - [x] Upgrade documentation to include more theory and be more comprehensive
-- [ ] Support for HTML-side templates for lightning-fast dom manipulation
+- [x] Support for HTML-side templates for lightning-fast dom manipulation
 - [ ] Support for multiple renderers for same virtualdom (subtrees)
 - [ ] Support for ThreadSafe (Send + Sync)
 - [ ] Support for Portals