Remove unnecessary yybegin calls

Figured out they were unnecessary after looking at Erlang.flex for
intellij-erlang.
Remove unnecessary state qualification
Eliminate COMMENT and WHITE_SPACE from bnf tokens

Use MergingLexerAdapter to filter out COMMENT and WHITE_SPACE from the
token stream that Elixir.bnf needs to handle.
Build grammar up from scratch to prevent freezing

Scrap Elixir.bnf's direct translation of Elixir.yrl because it caused
IDE to freeze.  Start over with support for the first token group in
elixir_tokenizer.erl, integers with different bases.  Additionally,
compress newlines + blank lines to just newlines, so Elixir.bnf doesn't
need to handle multiple EOL in a row.
Consume EOL at end of COMMENTs

Consume the EOL for COMMENTs so text in adjacent COMMENTs can be
appended while preserving newlines and so floating EOLs between COMMENTs
don't have to be handled.
Allow EOL at EOF to be optional
Strip EOL and white space from beginning of file
Add non-user-specific files from .idea

Based on https://intellij-support.jetbrains.com/entries/23393067.
Parsing tests
Sort static final TextAttributesKey
Add number highlighting
Color Settings Page

Custom the colors for Comments and Numbers.