version.sh: add FFMPEG_VERSION_{MAJOR,MINOR,PATCH} macros

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
tools/gen-rc: add source-dir as script argument

Prepare for generation of resources files at build time.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
lib*/Makefile: add $(DESCRPTION)

Will be used for dynamic Resources file generation.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Dynamic resources files generation in make-time

Rationale:
 * Reduce tree size for systems that don't need the .rc's.
 * Reduce working overhead (before this, every change made to .rc's needed
   to be first made to tools/gen-rc and then regenerate all)

Signed-off-by: Timothy Gu <timothygu99@gmail.com>