Fix bug in memcache sessions

Add support for field of type sql.NullXxx in rawSet.setFieldValue()

Fix Issue #3337

add GetProvider

Add Redis Sentinel session support

v1.11.1

Close fs when is not nil

format list in .travis.yml

panic when close nil filesystem

better format

- add comments for public function
- format import order in admin.go
- better format for NewControllerRegister in router.go

add different column name parse strategy

add context for db operation

Add .Elapsed in context.ResponseWriter for monitor purpose

With this commit we can record per requests's elapsed time,
so we can easy to monitor that by use a filter.

V1.11.0

#3192 AddTestSnakeString

Fix #3192

Lock