Make use of version_compare()
No need for returning the exploded version
Change role of parameter of peachyCheckPHPVersion()

The optional parameter was used to override the PHP version of the environment (unit testing purpose).

This commit makes the parameter to specify the minimum PHP version expected.
Make parameter of peachyCheckPHPVersion() mandatory

So that MINPHP constant is decoupled.

Also fixed phpdoc.
Merge pull request #37 from vlakoff/checkPHPVersion

Make peachyCheckPHPVersion() simpler and more useful