Fix Composer dependency reference

Installation instruction had a typo.
Merge pull request #15 from kix/patch-1

Fix Composer dependency reference
Update Use.md
Update Use.md
Update Extend.md
Counter verification added
Update HOTP.php
Update HOTP.php
Contributing
Tests added
getInitialCounter marked as deprecated
Doc updated
Typo
Update README.md
Code coverage support
Code coverage options changed
Code design
Code coverage options
Bug fixed
Update Contributing.md