Add option to link Boost dynamically (#1025)

Distributions can guarantee the existence of a specific version of
the Boost libraries, so it makes less sense to link them statically.
Use pkg-config over CMake to find Freetype (#1024)

If pkg-config does not exist on the build system, then the old
FindFreetype.cmake behavior will be fallen back upon, but pkg-config
should be a lot more reliable.