Reformat.
Issue #8: start implementing circular functions on complex arguments.
99○ should be a DOMAIN ERROR, according to the ISO standard.
Add another error test case.
Issue #8: implement ¯12○.
Issue #8: implement ¯11○.
Issue #8: implement ¯10○.
Issue #8: implement ¯9○.
Issue #8: implement ¯8○.
Issue #8: implement ¯4○ according to the ISO standard.
Issue #8: implement 0○, including an obvious extension to the ISO
standard when the result is complex.
Issue #8: implement 4○.
Issue #8: implement 8○.
Issue #8: implement 9○.
Issue #8: implement 10○.
Issue #8: implement 11○.
Issue #8: implement 12○.