We append an assembler identifier to generated code. For Merlin 32,
this was "_Merlin32". All of the other assemblers use a lower-case
string, which makes Merlin look a little weird, so it has been
changed to "_merlin32".
Windows filesystems are generally case-insensitive, so this won't
likely affect anything.
The new name is more indicative of the purpose of the directory.
Updated the docs to point out that you can delete the contents any
time you want, so long as SourceGen isn't running at the time.
Also, change the default column widths for the exporter.
