Adding HTTP_KWARGS as httplib2.Http(**HTTP_KWARGS)

This way e.g. the timeout parameter can be used through HTTP_KWARGS = {'timeout': 5} (Closes #14). 

It also alows adding additional 'ca_certs' or 'disable_ssl_certificate_validation' arguments useful for bug #11.

See also: http://bitworking.org/projects/httplib2/doc/html/libhttplib2.html#httplib2.Http