Reworking most heuristics to only return one match
Removing unused array of candidate languages.
Removing inconsistency of `find_by_heuristics` (was sometimes returning nil and sometimes returning and empty array)
Use heuristics earlier to inform the rest of the classification process
Moving comments
Bail earlier if the file is empty.

This will change behavior for empty files with unique extensions, returning nil instead of the language.
Remove more empty samples
remove reference to empty.js
Tests for BlobHelper#empty?
Merge pull request #1674 from github/rework-heuristics

Rework heuristics