update CodeMirror to 3.21

and require.js to 2.1.10

closes #4812
fix regex for cleaning old logs with ipcluster

it still had the 'z' suffix from ages and ages ago, so no files would ever match.

closes #4810
Fix typos in parallel doc
Fix inconsistencies in parallel direct interface doc

Running through the entire page would produce errors, as different
variable names were used, or, in the case of the %px a=b example, not
throw an exception because a and b actually were defined in an earlier
example.

The following fixes allow one to follow through the entire page and
experience the expected behaviors
Merge pull request #4823 from adamatus/parallel-doc-fixes

Minor fixes for typos/inconsistencies in parallel docs
Merge pull request #4819 from minrk/cm3.21

update CodeMirror to 3.21
Error in Session.send_raw()

Addresses issue ipython/ipython/#4839.
Added test_send_raw() for issue #4839, see pull request 4840
Removed debug prints
adjustments to notebook app logging

Mainly add a log_request function (from nbviewer) for formatting tornado access logs.

Relevant effects:

- demote successful access logs to DEBUG
- demote kernel connect messages to DEBUG

which reduces the noise at INFO-level (default)
Merge pull request #4840 from dsblank/master

Error in Session.send_raw()
Remove some leftover traces of irunner
Merge pull request #4844 from minrk/tornado-logs

adjustments to notebook app logging

Mainly add a log_request function (from nbviewer) for formatting tornado access logs.

Relevant effects:

demote successful access logs to DEBUG
demote kernel connect messages to DEBUG
which reduces the noise at INFO-level (default)
Merge pull request #4820 from minrk/super-old-z

fix regex for cleaning old logs with ipcluster
Reduce information about Pexpect
Merge pull request #4846 from takluyver/irunner-vestiges

Remove some leftover traces of irunner
fix tooltip token regex for single-character names

closes #4808
test tooltip tokens
Merge pull request #4851 from minrk/tooltip-re

fix tooltip token regex for single-character names