Add initial error tests.
Trigger help code paths.
Assert on signals module.
Assert on psargs (-- -ax).

Assert on -U option, remove -a when -u or -U is present.
Assert on -u option.
Assert on -c option.
Pass opts to callback in killer().

In case no opts are specified and the caller wishes to inspect the
arguments/options.
Assert on missing pid file error.

Assert on invoking killer with no opts.
Remove obsolete error.
Remove obsolete statement.
Assert on regexp pattern compile error.
Tidy match() signature.

Assert on EMATCH.
Tidy command handlers.
Assert on EREGEXP_COMPILE (kill).
Expect opts in match().
Expect opts in kill().
Ignore branches from coverage.
Assert on killer.kill() errors.

100% code coverage.
0.1.19