Updated composer.json and readme

Some docs and explicit dependency on PHP 5.5 for dev, PHP 5.3 for usage.
upgrade class references

utilize compile constants instead fo runtime reflection
change coverages for sensibility

some of the tests can't be covered internally
translation unit tests
fixed feature stack throwing errors on missing feature

get feature should return null if trying to get a feature that doesn't
exist.
translations feature
First pass on plex interface.