Refactor WebHandler syntax

Seal off this version's forward support in CI

Set new minimum ST version to 4149

Fix completion scopes

Reorg for v4.0.0

- Add a scope suffix to ASP.Net/WebForms to differentiate from Razor.

    + *Breaking change:* The Razor syntax now "owns" the `.cshtml` file
      extension. If you need it bound to WebForms-style pages, use the "Open
      all with current extension as..." option from the Syntax selector menu
      in the bottom-right.

    + This also means that completions and so on can be more easily targeted at
      one or the other syntax.

- Move some completions to snippets

    + *Breaking change:* The `exp*` completions have been removed in favor of
      typing the `<%*` expressions themselves.

- Enable autocomplete by default in ASP.Net, and on `@` for Razor.

- Razor gets comment block toggling (although it's not perfect).

Reorg for v4.0.0

- Add a scope suffix to ASP.Net/WebForms to differentiate from Razor.

    + *Breaking change:* The Razor syntax now "owns" the `.cshtml` file
      extension. If you need it bound to WebForms-style pages, use the "Open
      all with current extension as..." option from the Syntax selector menu
      in the bottom-right.

    + This also means that completions and so on can be more easily targeted at
      one or the other syntax.

- Move some completions to snippets

    + *Breaking change:* The `exp*` completions have been removed in favor of
      typing the `<%*` expressions themselves.

- Enable autocomplete by default in ASP.Net, and on `@` for Razor.

- Razor gets comment block toggling (although it's not perfect).

Fix orphaned `else`

Closes #3

Cut v3.0.0

Rename root scope to `embedding` like PHP

This lets people set color schemes that show embedding without being
overly cluttered.

Directive/ASHX work on Readme