Make it possible to add mpl.rcParams to itself or deepcopy

Before it was not possible to set all rcParams to mpl.rcParams or use
 copy.deepcopy on mpl.rcParams.

There were two problems:
 1. validate_bool_maybe_none(None) was raising ValueError
 -> fixed by accepting this value
 2. svg.embed_char_paths was deprecated by svg.fonttype but both have
 different valid values (bool vs strings).
 -> fixed by adding a "value translation" lambda to deprecatedmap
 which translates the boolean values to the string values of
 svg.fonttype.

Also changed all validators, which accept None to check strings
without case ("none" vs "None").

Test for this: mpl.tests.test_rcparams.test_Bug_2543()

Closes: #2543
fixes issue #2556

Fixes it in two ways:

1) changes the closure of `on_dpi` to be over a weakref, not `self`
2) cleans up the call back when the quiver is removed
pep8 fix
REF/TST: split up boxplot function into a calculator (cbook.boxplot_stats) and a drawer (axes.bxp).
Existing function now relies on these two functions.
BUG: fixed cbook tests for Python 2.6
ENH: allow for custom patch artist and labels to the boxplots
WIP: more tests and add option to toggle box

TST: added tests for all of bxp and more boxplot tests

TST: fixed boxplot baseline image

TST: added baseline images for bxp
DOC/REF: added docstring for axes.bxp and refactored all references to outliers as fliers
REF/TST: update boxplot_stats test with outliers changed to fliers

ENH/TST: boxplots stats now takes a labels kwarg

MNT: minor PEP8 whitespace fix
MNT: reran boilerplate.py
DOC: added blurb in changelog
MNT: got rid of build-breaking `u''` strings in pyplot
MNT: fixed changelog whitespace
ENH: cbook.boxplot_stats can now set the whiskers to -range- (min/max) or specified percentiles. If IQR is zero, min/max are used
TST: added tests and baseline images for new whisker behavior
ENH: added remaining bxp kwargs to boxplot
DOC: expanded boxplot_stats docstring
DOC: added examples
DOC: impoved example boxplot figure layout and confirmed that they build with docs
REF/TST: split up boxplot function into a calculator (cbook.boxplot_stats) and a drawer (axes.bxp).
Existing function now relies on these two functions.