add PheanstalkInterface
Fix documentation
Ignore vendor/ & composer.phar
Use type hint for setConnection
Fix Test about Connection
Add Test about PheanstalkInterface
Merge pull request #67 from armetiz/interface

The implied interface of `Pheanstalk_Pheanstalk` has been extracted into
`Pheanstalk_PheanstalkInterface`, which `Pheanstalk_Pheanstalk` now implements.