Deeply nested blocks and options lists

• Deeply nested blocks are now rendered correctly
• Options list regex no longer causes catastrophic backtracking
• Angle brackets and aliases have been fixed in the options list

Fixes #37
Fixes #40

Thanks to @asottile for contributing a fix for options lists.
Thanks to @chen19901225 and @asottile for reporting issues.
Thanks to @lextm for contributions to issue tracking.