* src/sdf/ftsdfrend.c (*): Added common renderer struct and
declaration of both the renderers.
* src/sdf/ftsdfcommon.h (*): Added common properties, typedefs,
macros etc.
* src/sdf/ftsdferrs.h (*): Error definitions for the module.
Added the necessary files required by the `sdf' module. These include files
for both the `sdf' and the `bsdf' renderers. Here is breakdown of what the
specific files will contain:
* src/sdf/ftsdfrend.*: Both the renderers.
* src/sdf/ftsdf.*: The rasterizer for the `sdf' renderer.
* src/sdf/ftbsdf.c: The rasterizer for the `bsdf' renderer.
* src/sdf/ftsdfcommon.h: Commmon properties and functions for both the
rasterizers.
* src/sdf/ftsdferrs.h: Common error define.
* src/sdf/sdf.c: For building a single object of the entire module.