Tokenize 'maybe' as an atom before OTP 25

[kvakvs]

Closes #1009

Need good review

Need assistance, because this has several problems

1. Switching SDK does not regenerate the editor with feature disabled or enabled, IDEA restart works. Need to invalidate all results of lexer somehow, when SDK changes.
2. Need a project instance to pass to new ErlangLexer() in
   1. org/intellij/erlang/search/ErlangFindUsagesProvider.java
   2. org/intellij/erlang/editor/ErlangSyntaxHighlighter.java

[ignatov]

Hi there! Thank you for the PR. From my personal experience, it's much easier to absorb all the changes into the grammar and highlight any wrong or outdated structures with a dedicated inspection.

[ignatov]

Ah, my fault. I see that one: https://github.com/ignatov/intellij-erlang/blob/master/src/org/intellij/erlang/inspection/Erlang25SyntaxInspection.java

And I got the idea – with the older versions we have to parse it as an atom. Hmm, maybe we can retoken it back in the parser. I'll think on how to do better.

[ignatov]

merged manually, thanks for your contribution