ADDS HOOK FOR XML MODIFICATION PRE-RENDERING

An XML filter can be defined as a function taking a single argument,
supplied as the 'svg' atribute of the graph (an lxml etree?) and
returning a modified version/copy thereof.

XML filters can be added to a plot using the new plot method
add_xml_filter(func).

The hook that executes any filters added to the plot, executes them in
order immediately prior to conversion to a string, in the class method
svg.render, and also immediately prior to returning a copy of the tree
in BaseGraph.render_tree
Merge pull request #78 from sirlark/xml_filters

ADDS HOOK FOR XML MODIFICATION PRE-RENDERING
Bump version
Fix a bug with secondary y-axis and formatted values

_y_2nd_labels will contain strings that will sometimes be human formatted and not cast-able to a float.
Merge pull request #85 from signed0/patch-2

Fix a bug with secondary y-axis and formatted values
Replace tooltip id with tooltip class. Fix #86
Merge branch 'master' of github.com:Kozea/pygal
Bump to 1.2.1
Add formatting to the DateY X axis label
Allow formatting other than the default for the X axis on the DateY plots.
This is done by setting
datey.x_label_format = "%Y-%m-%d"

The formatting is done by the strftime function, so any valid format will work.
See: http://docs.python.org/2/library/time.html#time.strftime
Fix value_formatter acces. It's not in config to_dict as it's a function.
Fix python 2 tests
Initial commit of Box Plot
Added tests for box, fixed regressions
Added vertical lines connecting whiskers to main box
Merge remote-tracking branch 'philt2001/master'
Merge remote-tracking branch 'jeffreystarr/add-boxplot'
Fix box plot
Bump
Fix median computation (s -> seq) and fix tooltips on box plot.
Bump 1.3.0