This adds support for the Eex templating that is used in the Phoenix
web framework. Eex files include HTML and Elixir code, and Elixir files
can include Eex in string literals marked with the `~L` prefix.
Additionally this unbreaks `"""` string literals, which did not work because
`"` was matched before `"""`
This commit allows using the <semicolon> expansion in commands, instead
of `\;`.
It makes commands look more elegant, and prevents new-comers from
falling into the trap of using <a-;> without escaping the semicolon.
