Add TOC nesting level option to hoedown_html_renderer

Closes #19.
Fix hoedown_buffer_printf on MSVC

Apparently "vsnprintf is included for compliance to the ANSI standard"
doesn't actually mean it's ANSI compliant.

Closes #21.
Release 1.0.2
GitHub style TOC anchor refs
Future-proof other options being used with the TOC renderer
All exposed structs are now opaque typedefs
Fix new repo URLs
Merge pull request #23 from penibelst/patch-1

Fix new repo URLs