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.
Use bool in normal_cmd().

Change signature of set_vcount_ca for consistency.
Use bool in do_mouse().

Change the signature of get_mouse_button() for consistency, and because
only do_mouse() uses it.
Use bool or int for local flag variables.

In do_pending_operator(), nv_zet(), nv_indent(), nv_g_cmd(), and more,
replace integer flags with bools when appropriate.

However, do keep the TRUEs and FALSEs of nv_cmds[].cmd_arg. It may store
values other than TRUE or FALSE, so it seems to make sense to use
integral constants.
Use bool in signatures of functions in normal.h.

Return bool from checkclearop, checkclearopq, add_to_showcmd,
find_decl, nv_screengo, get_visual_text, and unadjust_for_sel as these
functions all return either TRUE or FALSE or OK or FAIL, but not MAYBE.

Change to arguments toplevel of normal_cmd, check of
do_check_scrollbind, and locally and thisblock of finddecl, to bools as
they represent predicates.
normal.c: Replace last TRUE/FALSE/OK/FAIL's w/bool.
Merge pull request #923 from splinterofchaos/normal-bool

Use bool in normal.h and .c.