Heredoc

Non-interpolated heredoc.
Add heredoc highlighting
Extract ESCAPE token
Rename heredoc to charListHeredoc

Realized I was confusing Ruby and Elixir syntax in my head and treating
single quotes as meaning a literal string without interpolation support,
when in Elixir it actually means just a CharList, so add in support for
interpolation for charListHeredoc.  More renames to follow along this
line of reasoning.
Rename string to charList

Was thinking in Ruby where single quotes is a non-interpolated string;
in Elixir what I was calling string is a CharList and what I called an
interpolatedString is just a String, both CharList and String should
support interpolation.
Rename interpolated string to string

All strings are interpolated.  I mistakenly called it interpolated
because of me thinking of the Ruby terminology.
Rename interpolated heredoc to string heredoc

Interpolated name was influenced by Ruby, but all strings and CharLists
support interpolation, so rename to string heredoc since the
distinction between CharList and String is what is important.
Remove obsolete generated classes

Remove the interpolated classes that aren't needed anymore since the
CharList + String renames.
Rename Interpolated String to String in Color Settings
Merge branch 'bug/limited-interpolation'