Don't export newApiError (it should never be called externally)
Initialize api in init() function in test file

* Allows testing of api queries in isolation
Add tests for GetUser and GetTweet
Move file containing examples to example_test.go
Separate example function and testing functions into different files
Fix retry logic when receving a rate-limit error in throttledQuery()
Implement GetFollowersListAll and corresponding test
Add examples for rate-limiting, cursor handling, client initialization
Attempt to prevent blocking when re-adding query to queue