Add OAuth driver

[hiendv]

No description provided.

[coveralls]

Coverage decreased (-5.4%) to 94.609% when pulling bc03573 on add-oauth into b09d184 on master.

[hiendv]

Interesting

# github.com/hiendv/gate/oauth
/tmp/go-build957966995/github.com/hiendv/gate/oauth/_test/_obj_test/oauth.go:51: cannot use DefaultProvider literal (type DefaultProvider) as type Provider in argument to driver.setProvider:
	DefaultProvider does not implement Provider (wrong type for Exchange method)
		have Exchange("github.com/hiendv/gate/vendor/golang.org/x/net/context".Context, string) (*oauth2.Token, error)
		want Exchange("context".Context, string) (*oauth2.Token, error)
FAIL	github.com/hiendv/gate/oauth [build failed]

[coveralls]

Coverage decreased (-6.9%) to 93.103% when pulling ca724ca on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-6.9%) to 93.103% when pulling ca724ca on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-6.8%) to 93.158% when pulling 967fd4f on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-6.8%) to 93.158% when pulling f0fbe65 on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-2.9%) to 97.135% when pulling 2c397a5 on add-oauth into b09d184 on master.

[hiendv]

Documentation and examples are required before merging.

[coveralls]

Coverage decreased (-2.9%) to 97.135% when pulling bd70743 on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-2.9%) to 97.135% when pulling bd70743 on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-2.9%) to 97.135% when pulling bd70743 on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-2.9%) to 97.135% when pulling c75c837 on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-2.9%) to 97.135% when pulling c75c837 on add-oauth into b09d184 on master.

[coveralls]

Coverage decreased (-2.9%) to 97.135% when pulling c75c837 on add-oauth into b09d184 on master.