Suggested by Brecht Van Lommel and Campbell Barton through code review comments.
Previously style modules were external Python script files whose absolute paths
were kept in .blend files. Now style modules are stored in .blend files as text
datablocks.
Style modules are configured in three steps:
1. Open an external style module file (or create a new text datablock) in the
Text Editor in Blender.
2. Add a style module to the list of style modules (by pressing the "Add" button)
in the Render Layer properties window.
3. Click the name entry and select the style module from the drop-down menu.
and RNA for it independent of the build flag for enabling Freestyle. Suggested
by Sergey Sharybin through a code review of the branch.
* Many #ifdef WITH_FREESTYLE blocks were removed to always have Freestyle-specific
DNA file specification and RNA for it built in Blender. This will allow Freestyle
setting survive even when a non-Freestyle build is used for loading and saving
files. It is noted that operations are still conditionally built through #ifdef
WITH_FREESTYLE blocks.
* To this end, new blenkernel files BKE_freestyle.h and intern/freestyle.c have
been added. All API functions in FRS_freestyle_config.h as well as some of those
in FRS_freestyle.h were moved to the new files. Now the relocated API functions
have BKE_ prefix instead of FRS_.
