Originally there was an infinite loop issue that was patched in issue
#308.  Unfortunately, it was fixed all the way.  This fix patches the
infinite loop fix to only add an offset to the `right_listindex` when
it is in a infinite loop scenario.

The last few extensions were updated to accept dicts/**kwargs as configs and more
tests were updated. Also updated extra to actually accept configs.

Note that extra requires an extra level of dicts. First you need
to indicate tha the settings are for extra, then, which extension
extra wraps. I'm not crazy abount this, bit not sur ehow else to do it
without making all the configs a global attribute on the Markdown class
to that any extention can access any other extensions config settings.
I don't think we wnat to do that.

Also updated extra to use dot notation for the sub-extensions.

All named extensions now use python dot notation in the tests - including
all builtin extensions (eg: 'extra' => 'markdown.extensions.extra'). This
is in anticipation of #336.

Note there are a few tests (in the error tests) that will still need
updating, but not till we make the change as they will test for the
new error message.