Merge Filament's math library

This math library was derived from Android's and is API compatible.
It adds new useful types (quat and half) as well as many missing
functions and optimizations.

The half type (fp16) is going to be used for HDR/color management.

Test: mat_test, quat_test, half_test and vec_test

Change-Id: I4c61efb085d6aa2cf5b43cdd194719b3e855aa9b