Rename RWTS18 format to RW18 in crackle.

This matches the name given to it by Roland in his source files.
Bump version number up to 0.2

0.1 was used for the initial release of the buildable PoP fork.
crackle now supports RW18 based 5.25" .nib files.

I added support for creating .nib 5.25" disk images which have tracks
encoded with the RW18 format.  Previously it only supported Apple's
RWTS16 format.

I also cleaned up various issues in the crackle utility that I
encountered while writing and testing this new RW18 functionality.

The biggest such change was removing the use of a sector value in RW18
script lines.  The tool now just accepts a intraTrackOffset which is
the same thing utilized in the PoP USR directives for writing out
object files in RW18 format.  This requires updates to the disk layout
scripts used to build Prince of Persia disk images.