Params map has string as key

Related to issue #540 and commit 3c22ca7c84456b19f2a017719b1533902594e672
Merge pull request #609 from bjornerik/bug/params-map

Params map has string as key

* bjornerik/bug/params-map:
  Params map has string as key
Enable descriptive header IDs.

Enable blackfriday.EXTENSION_AUTO_HEADER_IDS to generate the name of the
header ID from the text in the header. Works for prefix and underline
headers.

- TOC extraction had to be modified to look for `<li><a href="#`>
  instead of `#toc_` because of this change.
- Fixed a number of tests that depended on the presence of `toc_` with
  as an `id` or as a `href` value.
Merge branch 'auto-header-ids' into local-version

* auto-header-ids:
  Enable descriptive header IDs.