feature-request: new option to skip headlines

[FlorianWendelborn]

Since I like to include a ## Table of Contents headline above the TOC it is inlcuded in the TOC too, which looks stupid.

I would suggest an option to skip the first n headings.

[betrue12]

If you use h1(#) or h2(##), you can avoid it as below!

Table of Contents (h1)
====

Table of Contents (h2)
----

[FlorianWendelborn]

@betrue12 nice workaround, but unfortunately it looks bad to humans then. 😄

[ponsfrilus]

Related to #60