Does not skip commented sections

[janrod]

When some sections in the document are commented they are still included in the TOC. They should be skipped.

[myurasov]

Adds my python comments to TOC – frustrating...

[flakrat]

Same with Shell examples:

## Command run as root, this command and the following line will be treated as an H2 and H1 by markdown-toc
# systemctl reboot

## Command run as normal user 
$ uptime