Support more binary assignment operators in templates (#39)

* Support more binary assignment operators in templates

angular/angular#62064

@deathaxe does this look about right?

* add test

* update precedence

* Update NgxHTML.sublime-syntax

Co-authored-by: deathaxe <16542113+deathaxe@users.noreply.github.com>

* Update NgxHTML.sublime-syntax

* augmented

* test augmented

* test output with assignment

* fix test

* test output with augmented assignment

* expand selection

---------

Co-authored-by: deathaxe <16542113+deathaxe@users.noreply.github.com>

Add support for template strings

This commit adds basic support for untagged and tagged template strings.

Regular expressions are highlighted using ST's RegExp (Basic) syntax
as a dedicated JavaScript specific regexp syntax is far inferior, especially
with regards to supporting interpolation.

Add CSS/HTML syntax highlighting in tagged template strings

This commit adds syntax highlighting in `` css`...` `` and `` html`...` ``
tagged template strings.

Add support for template strings

This commit adds basic support for untagged and tagged template strings.

Regular expressions are highlighted using ST's RegExp (Basic) syntax
as a dedicated JavaScript specific regexp syntax is far inferior, especially
with regards to supporting interpolation.

Extend meta.expression scope

This commit adds `.expression` sub-scope name to distinguish embedded
interpolation expressions from control flow statements.

Add a global `meta.template.ngx` scope

This commit scopes whole document `meta.template`.

Various template syntaxes make use of it to be able to use simpler snippet or
completion selectors across all supported languages (e.g.: CSS/JS/HTML).

Assign ngx file extension

This commit assigns *.ngx file extensions as Angular Playground detects it
and assigns special syntax, too.

Remove redundant lookbehind (#27)

This commit removes not required lookbehind `(?<=\@)` in `angular_blocks`
variable, which just causes incompatibility with ST's custom sregex engine.

add simple highlight for @let

update readme