cleanup stale, unused exceptions in parallel.error

closes #2044
ensure raw_input returns str in zmq shell

matches raw_input.  Some things can't handle unicode objects (e.g. `help()`).

closes #1145
allow cython cache dir to be deleted

workaround by clearing the distutils mkpath cache,
which prevents it from ever creating a given path more than once.

closes #3010
respect image size metadata in qtconsole

This doesn't mean retina support, as image data is actually resampled, unlike in a browser.
use smooth transform in QtConsole
Fixing issue preventing the correct read of images by full_html and reveal exporters.

Currently to see and images in the notebook inside a md cell you can use the prefix files/ to read the content of the directory where the ipynb lives. But, if you do a conversion using full_html or reveal exporters, the are not rendered ok because the previous version of this function erased `/files/` instead of `files/`. With this fix, the html files produced by full_html and reveal exporters can read the images in a correct way.
fix `file/` URL replacements in nbconvert
open markdown links in new tabs

restores earlier behavior lost when we switched to marked.

closes #3439
move ipython sphinx extensions into IPython.sphinxext
Python 3 print functions

allows apigen to run on Python 3
remove trivial nbconvert example
Merge pull request #3557 from minrk/target_blank

open markdown links in new tabs
Merge pull request #3550 from damianavila/patch-1

Fixing issue preventing the correct read of images by full_html and reveal exporters.

only strip `file/` at begining of URL.
Merge pull request #3541 from minrk/qtimgsize

respect image size metadata in qtconsole

This doesn't mean retina support, as image data is actually resampled, unlike
in a browser.
Merge pull request #3529 from minrk/rawin

ensure raw_input returns str in zmq shell

matches raw_input. Some things can't handle unicode objects (e.g. help()).

closes #1145
Merge pull request #3527 from minrk/parallelerror

cleanup stale, unused exceptions in parallel.error
Merge pull request #3540 from minrk/cythoncache

allow cython cache dir to be deleted

workaround by clearing the distutils mkpath cache, which prevents it from ever
creating a given path more than once.
mention double-control-C to stop notebook server

in the initial log message.

closes #2971
Merge pull request #3564 from Carreau/rm-armor

Remove trivial nbconvert example

This used to be just to test the templating engine and survived nbconvert merge into IPython.
Merge pull request #3566 from Carreau/fix-event-name

fix event names