Update ARCHITECTURE.md

Clean up typos. Exciting project!
Refactor attribute values

Attribute values are no longer represented as arrays in the AST. Instead
an attribute value is either a TextNode or MustacheNode. If the
attribute contains both text and mustache parts, they are concatenated
via the CONCAT helper. Examples:

- class="btn-large" parses as `text("btn-large")`
- class="{{status}}" parses as `mustache("status")`
- class="btn-large {{status}}" parses as
  `mustache("CONCAT", params: [string("btn-large "), id("status")])`

Consequently, the ATTRIBUTE hook no longer accepts arrays and instead
expects a value.
Merge pull request #25 from briandunn/patch-1

Clean up some documentation typos
Merge pull request #24 from mmun/unwrap-sexprs

Attribute value refactor
Sync simple-html-tokenizer

Sync simple-html-tokenizer to commit fa0717334a389e43342ee40ecd25d560003f1962.
Rewrite elements with hyphenated tags as blocks

`<x-foo src="{{src}}"></x-foo>` becomes `{{#x-foo src=src}}{{/x-foo}}`
`<x-foo src="{{upcase src}}"></x-foo>` becomes `{{#x-foo src=(upcase src)}}{{/x-foo}}`
`<x-foo src="a{{b}}c{{d e}}"></x-foo>` becomes `{{#x-foo src=(concat "a" b "c" (d e))}}{{/x-foo}}`