Add xsnprintf()/xsvnprintf() wrappers

Start replacing calls to sprintf() to use these.
Audit:  libs/FRenderInit.[ch]

* Reindent
* Replace sprintf() with xsnprintf()
Audit:  libs/FRenderInterface.h

* Prototype changes to remove explicit naming of types
Audit:  libs/FScreen.[ch]

* Reindent
* sprintf() -> xsnprintf()
Audit:  libs/FShape.[ch]

* Reindent
Audit:  libs/FTips.[ch]

* Reindent
Audit:  libs/Fcursor.h

* Reindent