Instantiated a new db object in each API call.

The object is not thread-safe, so calling a function on it from more
than one API call at once would break things pretty badly.
Merge pull request #23 from bikeshare/api_fix_hang

Instantiated a new db object in each API call.
Added Get-All-Bikes API function.
Added Get-All-Users API function.
Tweaked comments.
Merge pull request #26 from bikeshare/api_func_add

Add API functions
Merge branch 'modularStart'