v0.12.2

This is a minor release, mainly adding functionality to build PCA models (include/eos/pca/pca.hpp).

This will be the last version that supports gcc-5, clang-3.x, and VS2015. The next release will require >=gcc-7, >=clang-5 and >=VS2017U3.

Other minor changes:

• Fix for texture mapping into destination image 6875e08
• Fixed some missing inlines, added lots of const, improved documentation, updates of submodules
• gcc-4.9 support removed