Evas filters: Implement advanced text effects

Add a new module in Evas to implement text effects.
The basic idea is to create some buffers (alpha/rgba),
draw some text into them, and apply various filters in a
sequential way.

A small script language allows you to set a filter to a
text object. This can then be passed through an Eo API
or using Edje directly (under the field description.text.filter).

Right now, the software engine should work fine, but GL rendering
suffers from a few limitations (no scaling and no proxy rendering,
which means a few effects might not work well).

More documentation will follow, and examples as well.

But, please bear in mind: this is a HIGHLY EXPERIMENTAL feature.
I'm including it to EFL 1.9 so that people can play with it,
but it should not be considered stable at this point in time.