Resolve issues with rule 16

[SecondSkoll]

Fix rule16 to reduce processing time on MD code blocks

Addresses #49

[ru-fu]

Could you explain what your trying to do in the regex? That would make it a lot easier to review and spot where it might go wrong.

Also, this rule won't catch code blocks that are created without explicit markup (through indentation).

[izmalk]

I can confirm that this change solves an issue of Vale hanging when trying to process something in the https://github.com/canonical/kafka-operator docs. With the fix, vale produces the result quite fast.

[SecondSkoll]

Processing issue seems to have been resolved. Using time make vale now results in:

real    0m1.352s
user    0m1.313s
sys     0m0.160s

Rather than having to stop it after 20+ minutes:

KeyboardInterrupt
make[1]: *** [Makefile.sp:115: sp-vale] Interrupt
make: *** [Makefile:30: vale] Interrupt

real    22m53.559s
user    22m54.040s
sys     0m1.188s

[ru-fu]

I'm okay with the changes to fix/unblock the current processing, but the rules will need to be revisited.

[evilnick]

👍