Add support for Yacc (.y) and Lex (.l) files

[SaZiKK]

Hello!

I'm currently working on compiler front-ends and spending a lot time on Yacc (.y) and Lex (.l) files. Yacc and Lex are commonly used tools for automatically generating compiler front-ends, so I hope WakaTime can add support for them. Now they are recognized as "Other"

Thank you.