Add support for Tokens API endpoints

[morgant]

A client of mine has a Ruby app that needs to manage their MapBox API tokens, so it'd be helpful if the Ruby MapBox SDK supported the Tokens API.

[morgant]

I'm currently exploring adding such support.

[morgant]

Okay, I think I have my implementation feature-complete (with the exception of temporary tokens) and ready to submit a PR, but I've got a couple questions first:

1. I stuck with this gem's method naming conventions, so #token_get, #tokens_list, #token_create, #token_update, #token_delete, #scopes_list, but would it be preferable to use #get_token, #list_tokens, etc.?

2. Some methods use a username parameter, but would it be preferable to make it an accessor like access_token?

3. I added tests, but they actually create/update/delete tokens (the tests clean up after themselves). Should I remove/comment out the tests?

[morgant]

@samfader Any input is welcome.

[samfader]

@morgant Great news!

1. I think the latter is better (#get_token). Most of the other endpoints in this gem don't have similar methods, which ones were you referring to when thinking of naming conventions?
2. I would keep it as a parameter.
3. Is it possible for you to mock those tests instead?