Correct a couple of signatures in engine/keys.c
Add some comments to engine/keys.c
A couple of variable renames in engine/keys.c

For better readability.
Rename internal functions of engine/keys.c
Improvements for variable uses in engine/keys.c
Add curly braces and empty lines to engine/keys.c
Fix processing of marks command in rhs of a map

Thanks to filterfalse.
Merge branch 'fix-multikeys-in-map-rhs'

Fix processing of marks command followed by anything in right-hand
side of a mapping.

Thanks to filterfalse.