Fixes #253

This patch contains these changes:

* Add 50+ new Ruby tests for method name/operator override matching.
* Unicode method names are now supported (#253).
* `=` method name postfixes are now supported.
* These operator overrides are now supported:
  `<`, `<=`, `!` `!@`, `~@`, `!`, `!=`, `!~`, `=~`
* The `<>` "operator" override is removed. It appears that this was
  a typo in the regular expression (`<=?>` should have been `<=>?`).

Syntax verified with https://docs.ruby-lang.org/en/2.7.0/syntax/methods_rdoc.html

This introduces support for some missing features to the Handlebars lexer:
Partials and path segments. Partials mostly appeared to work before, but the
`>` in `{{> ... }}` would appear as a syntax error, as could other
components of the partial. This change introduces support for:

* Standard partials: `{{> partialName}}`
* Partials with parameters: `{{> partialName varname="value"}}`
* Ddynamic partials: `{{> (partialFunc)}}`
* Ddynamic partials with lookups: `{{> (lookup ../path "partialName")}}`
* Partial blocks: `{{> @partial-block}}`
* Inline partials: `{{#*inline}}..{{/inline}}`

It also introduces support for path segments, which can reference content in
the current context or in a parent context. For instance, `this.name`,
`this/name`, `./name`, `../name`, `this/name`, etc. These are all now tracked
as variables.