extend OAuth support

~~OAuth for bots/scripts at least.~~

Implicit grant would be really nice as well (generating a URL for someone who is using the module indirectly).

see docs:
https://github.com/reddit/reddit/wiki/OAuth2
https://github.com/reddit/reddit/wiki/OAuth2-Quick-Start-Example

BTW, PRAW (the python reddit wrapper) is a good example too look at regarding OAuth token usage.
