Added alternative implementation for ProDOS 8 I/O buffer management. The purpose...

Added alternative implementation for ProDOS 8 I/O buffer management. The purpose of this implementation is to avoid pulling in the heap stuff (and especially the C-written posix_memalign() function) into small file utility-like applications. It saves in this scenario > 1400 Bytes. It manages memory blocks between $0800 and the cc65 start address. This is especially usefull for the now supported "native" SYS programs starting at $2000.

git-svn-id: svn://svn.cc65.org/cc65/trunk@4210 b7a2c559-68d2-44c3-8de9-860c34a00d81