CMake improvements and cleanups

Add missing "-msse" flag, clean up old BUILD_SHARED flags (cmake has its own
system for doing this) and add a couple more build targets.
Add readme file for cmake building.

This adds a simple readme file for building the cmake project.
It includes the most common flags and quick build/install commands.
Merge pull request #4 from katajakasa/ttv-cmake-improvements

CMake readme+improvements