Adding support for custom user agents
adding the headers to the session instead of to each post/get for requests
fixing the terribleness on my previous submit >.<
Removing extra spaces
Changing how the formatting of self.user_agent is done to be simpler.
Moved the user_agent definition out of the constants file and into evelink.__init__.py
Added requests test case for UA
Removed an unnecessary intermediate variable from evelink.__init__
Removed an unnecessary import from evelink.api
Updated the tests to use the user_agent from evelink.api
Merge branch 'feature_custom_useragents' of git://github.com/Regner/evelink into master

Conflicts:
	evelink/api.py
	tests/test_api.py
Add user agents for AppEngine requests as well