Add support for SETEX command
Update README

Update README to add support for SETEX redis command.
Fix README to mention ability to create mock class without throwing an
exception (issue #20)
Cleanup and enhance unit tests

Cleanup and enhance unit tests with better use case testing for SETEX.
Fix README.
Fix markdown
Fix README markdown
Merge branch 'del-multiple' of github.com:dchancogne/RedisMock

Conflicts:
	tests/units/RedisMock.php
Merge pull request #21 from dchancogne/master

Add support for SETEX command