Add (-) function for Fin
Change to infix form
Added documentation for the effectful file operations.
Add splitAt to Vect
Allow resolving metavariables from ibcs
Efficiency of coverage check

Instead of checking fully elaborated definitions, make sure we only
check cases which the programmer has written explicitly - other cases
are ruled out by unification. Fixes #975

I had thought I had done this a while ago, but it turns out I didn't do
it properly! This should make many pathological coverage checking
examples significantly quicker.
Merge pull request #1022 from jfdm/documentation-effects-file

Added documentation for the effectful file operations.
Merge pull request #998 from jedesah/substract_fin

Add (-) function for Fin
Merge pull request #1023 from jedesah/vect_splitAt

Add splitAt to Vect