Resolves #892.

cElementTree is a deprecated alias for ElementTree since Python 3.3.

Also drop the recommendation to import etree from markdown.util,
and deprecate markdown.util.etree.

Note: this slightly changes existing behavior in that raw HTML tags are no
longer included in the HTML `.toc`. However, the fact that that worked before 
was an oversight. The intention was always to strip all markup. Resolves #899.

Addes a new `permalink_title` option to the TOC extension, which allows the title attribute of a permalink to be set to something other than the default English string "Permanent link".
Fixes #781.

Two new configuration options have been added to the toc extension: 
`anchorlink_class` and `permalink_class` which allows class(es) to be 
assigned to the `anchorlink` and `permalink` HTML respectively. This 
allows using icon fonts from CSS for the links. Therefore, an empty string 
passed to `permalink` now generates an empty `permalink`. Previously 
no `permalink` would have been generated. Based on #776.

Tox has already been removed from `make test` and is no longer recommended
for testing in the contributing guide. Additionally, the extra tests it runs
(checking the spelling of documentation, etc) are of no value to end users.
As things are currently set us, tox is only used on the Travis CI server.
Given the above, there is no reason to include it in the release tarball.
Closes #808.

Fixed #812.

The slugify function will stript the STX and ETX characters from
placeholders for backslash excaped characters. Therefore, we need
to unescape any text before passing it to slugify. Fixes #864.

Ensures anyone still using Python 2 gets a readable error message.
This does not specify a specific version number to remove the maintenance
burden of updating it with each future release. It will likely get removed
in the next few releases as it will have served its purpose by then.
Fixes #871.