[Feature] Pedantic mode.

[ixchow]

Have a mode -- pedantic mode -- that checks for (and warns/disallows) for things like:

Synonym misuse:

• knitting with no carriers (should be 'drop')
• split with no carriers (should be 'xfer')
• tuck with no carriers (should be 'amiss')

Useless operations:

• knitting on an empty needle (should be 'tuck')
• xfering no stitches
• dropping an empty needle (yes I realize this is actually useful sometimes)

Dangerous operations:

• stretching yarn really far with racking
• stacking many many loops (user-configurable limit?)

Pedantic mode should probably be able to be set/unset easily, to allow for functions that "know what they are doing".

What else?