Parameter Editor mode. This is a WIP commit. Only the base line
color, base alpha transparency, and base line thickness are respected.
More additions are anticipated to account for other parameters.
* Added FRS_finish_stroke_rendering() to clean Freestyle-related
temporary resources after stroke rendering.
* Some functions in FRS_freestyle.cpp are now declared as static
functions, so as not to mess up the program-wide name space.
* Made the StyleModule class inheritable, and defined new subclass
BlenderStyleModule that takes a Text object instead of a file name.
