Help text improvements.
Check backends for support of unknown cell size.
Add GAS intel mode assembler output.

This has been added to the nasm generator currently and has the same
limitations.
Split 'gas' changes from linkage changes.

Which means we can now create an assembly file that can be complied with
nasm and linked using the system C compiler. This works on the current
FreeBSD.
Grab the BFBasic hack from the history...

... and add an option for it.
Memory size option made common.

This doesn't apply to "running now" which will still use the huge RAM
method. But if that's not available or when running later the '-mem'
option now specifies how many cells to allocate.
Merge all the tape length setting options onto one.

Also add the setting to the few that don't already have it.