Add test for lines with trailing whitespace.

Trailing whitespace should not interfere with normal indentation algorithm.
Emit semicolon in case of trailing whitespace.

Lines ending like `\s+$` should not impact indentation of subsequent
lines. Instead, the trailing whitespace should be tokenized as if it
didn't exist.
Add file-local variable to avoid whitespace cleanup.
Merge pull request #99 from elixir-lang/tokenize-whitespace-eol

Tokenize trailing whitespace properly. Fixes #97