cached parser

[greut]

This addresses the #30 issue. It proposes a cache for the .editorconfig definition

master branch running on https://github.com/dotnet/roslyn

$ time editorconfig $(git ls-files) | wc -l
680099

real    0m7.575s
user    0m8.568s
sys     0m0.764s

this branch

$ time editorconfig $(git ls-files) | wc -l
680099

real    0m1.862s
user    0m1.912s
sys     0m0.402s

Previous discussions were made under #48 - Kudos go to @andreynering for the useful reviews and feedbacks.

[andreynering]

Seems great! 👏

Just a TODO comment missing

Thanks! 😉