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.

packages/rsx/src/error.rs

@@ -0,0 +1,56 @@
+use std::fmt::Display;
+
+use dioxus_core::OwnedCodeLocation;
+use serde::{Deserialize, Serialize};
+
+/// An error produced when interperting the rsx
+#[derive(Debug, Serialize, Deserialize)]
+pub enum Error {
+    ParseError(ParseError),
+    RecompileRequiredError(RecompileReason),
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub enum RecompileReason {
+    CapturedVariable(String),
+    CapturedExpression(String),
+    CapturedComponent(String),
+    CapturedListener(String),
+    CapturedAttribute(String),
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct ParseError {
+    pub message: String,
+    pub location: OwnedCodeLocation,
+}
+
+impl ParseError {
+    pub fn new(error: syn::Error, mut location: OwnedCodeLocation) -> Self {
+        let message = error.to_string();
+        let syn_call_site = error.span().start();
+        location.line += syn_call_site.line as u32;
+        if syn_call_site.line == 0 {
+            location.column += syn_call_site.column as u32;
+        } else {
+            location.column = syn_call_site.column as u32;
+        }
+        location.column += 1;
+        ParseError { message, location }
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Error::ParseError(error) => writeln!(
+                f,
+                "parse error:\n--> at {}:{}:{}\n\t{:?}",
+                error.location.file_path, error.location.line, error.location.column, error.message
+            ),
+            Error::RecompileRequiredError(reason) => {
+                writeln!(f, "recompile required: {:?}", reason)
+            }
+        }
+    }
+}