Add flag to optionally respect original header indent

[ericdorsey]

Say markdownanchormaker finds the following headers:

$ ./markdownanchormaker.py -f /tmp/foo.md
Headings found in /tmp/foo.md:

# Table Of Contents
# Foo Commands
### Foo Help
## Chapter 1: Intro To Foo
### Foo's Cousin Bar
### Foo's Cousin Baz

Add a flag (say -k / --keep-indent?) that respects "subheadings" from the original document, and inserts nbsp;'s into the generated inline links to semi-emulate the subheadings.

So ### Foo Help might become    [Foo Help](#foo-help) -- ie, if number of #'s > 1, add an   for each # (If it's just one # we leave it alone, as it's the biggest header / stays fully flush left)

• MAYBE: Optionally also allow how much indent per #?..