Package fewer files in the gem

[teeparham]

• Do not distribute test files
• Do not distribute the intermediate api_names_out.yaml file

Reduces the packaged gem size from 1.8Mb to 1.6Mb

The practice of not distributing test files with a gem was originally
discussed and adopted by the Bundler team here:
rubygems/bundler#3207

[coveralls]

Coverage remained the same at 94.737% when pulling 5ce622c on teeparham:test-files into 0bb3352 on google:master.

[icco]

Thanks!