Add endpoint to return valid i-Tree codes by i-Tree region

Also `gitignore` artifacts generated by `make`
Merge pull request #43 from RickMohr/get-itree-codes-endpoint

Add endpoint to return valid i-Tree codes by i-Tree region
Ignore build relics
Merge pull request #44 from steventlamb/topic/ignore_build_relics

Ignore build relics