Allow setting type of Real at compilation time

Use a REAL preprocessor definition.
Pass it from the Makefile in variable DEF

Can change using `make DEF=REAL=X`

Also allowed changing bounds with arguments in main.
Probably not that useful. Might remove later.

Tried to make a tester that overlays a series of BMPs but
the RenderBMP -> ScreenShot approach only works once; subsequent attempts lead to entirely filled images.