Use bool for flags in oparg_T.

Several opart_T members like use_reg_one, end_adjusted, empty,
is_VIsual, and block_mode, only ever store TRUE or FALSE, so make this
constraint explicit by changing them to bools, and TRUE to true and
FALSE to false in the context of their uses.

The member, inclusive, has several other uses such as in arithmetic
equations and one inequality, but every single assignment (obtained with
'grep -r "inclusive \\="') sets it to either TRUE or FALSE.

This also implies that the inequality, "oap->end.coladd <
oap->inclusive", can only be true when coladd==0 and inclusive==true, so
test for that instead.

For consistency, change the first argument of findpar (which ends up
being inclusive) to bool.

Include stdbool.h for consistency with issue #918.

This commit shrinks the size of oparg_T from 128 bytes to 112 (-13%) on
my machine.