Switch a bunch of migrated tasks to read option values the new way.

Review Request #1281 - Created Nov. 4, 2014 and submitted

Benjy Weinberger
johanoskarsson, lahosken

Note that this also allowed us to get rid of some explicit fallbacks
to the config file, as new options do this automatically, assuming
the right naming conventions.

Some configs were renamed and added to the config migration script,
to align them with these conventions.

Note that this slightly changes the semantics of one flag. Previously
--extension in MarkdownToHtml would overwrite the default values of
['.md', '.markdown']. Now it appends to those two defaults. So the
default extensions will always be processed, plus whatever is added.

If this is an issue, please mention it in the review!

CI pending.

Larry Hosken
Benjy Weinberger
Review request changed

Status: Closed (submitted)

Change Summary:

Submitted as ee0732a42bdd614baf0e065326f1f6872a041d3a.