add titleweight rc param
actually read the new rcParam
reference rcparam in docstring for pyplot interface
fix pep8 errors.
MultiCursor: make events connected during __init__ accessible (for later removal)
fix initialization of AnnotationBbox where None values of xybox and boxcoords parameters are not correctly handled.
make event connector ids private
Fix infinite recursion in units with ndarray subclasses.

This was partially addressed for masked arrays in #2290. However,
this does not work for all ndarray sub-classes, like the quantities
package. The fix here is to make sure ravel is actually succeeding
in changing the shape of the object. If it doesn't just return
what we've got.
Merge pull request #2591 from dopplershift/fix-infinite-recursion

Fix infinite recursion in units with ndarray subclasses.
Merge pull request #2579 from megies/mutlicursor_store_connectors

MultiCursor: make events connected during __init__ accessible (for later removal)
Merge pull request #2574 from adrn/titleweight

Add axes.titleweight as an rc param
Merge pull request #2582 from leejjoon/fix_annotation_bbox_default

fix initialization of AnnotationBbox
Add easy style sheet selection.
Add rc_params_in_file to return partially-filled RcParams

This allows style sheets to update the current settings instead of overwriting them.
Rename style files to `*.style`
Allow style.use to open URLs
Remove pyplot import
Add style context manager and tests
Change style extension to *.mplstyle
Got a little crazy with the whitespace