Implement highlight support for all regex delimiters

[mattdeboard]

Elixir allows 8 different delimiters for regex:

~r/hello/
~r|hello|
~r"hello"
~r'hello'
~r(hello)
~r[hello]
~r{hello}
~r<hello>

We should support proper highlighting for each of these.

[mattdeboard]

Completed by #60