Enable using provider specific parameters

Allow for use of provider specific optional parameters on auth init,
such as Twitter's force_login or Facebook's auth_type.
Provide specific parameter bug fixes

Fix 1) AUTH_OPTIONAL_PARAMS reference in example handlers, 2) coding
utf-8 line, 3) Changed optional_params check to test for dict type.
Provider-specific params - example handlers bug fix

Fix AUTH_OPTIONAL_PARAMS reference again
Merge pull request #35 from jchu1/master

Provider-based extra optional parameters for auth init.