Solved issue #426 
Changed flavors of pure data to Purr Data's relationship to Pure Data
and relocated it below goals.

Shifting flavors of pure data below goals and renaming it.

Fixed Typo from "Pure Data" to "Purr Data"

Fix up the install/uninstall targets to properly handle the case that the build directory doesn't exist.

Add convenience targets to the toplevel Makefile which install additional abstractions and externals after a light build. E.g.: make light pdlua_ext