Pretty print JSON data

See travis-ci/travis-ci#1555.

JSON data are pretty-formatted for humans.
Accept `pretty` parameter for pretty formatting

If the parameter is equal to `true` (in any case--`TRUE`, `True`) or
a positive integer, return pretty formatted JSON data.

No tests are necessary.
Account for absence of `pretty` parameter
Add specs for pretty print JSON

They only check that the response includes `\n`, which should not happen
otherwise.
Merge pull request #97 from travis-ci/core-gh1555-pretty-print-json

Pretty print JSON data
change readme with test db command
Merge pull request #102 from rainsun/change-readme-with-test-db-command

Update README with new schema loading command
Use core from ps-tags-and-branches
Bump travis-core
Run 'bundle exec' for DB task

See https://travis-ci.org/travis-ci/travis-api/builds/17125195
Merge pull request #104 from travis-ci/ha-bug-ci_fix_1

Run 'bundle exec' for DB task
Use travis-api from master branch