Fix manual contour label positions on sparse contours

Prior to this, contour labels were positioned at the nearest contour
vertex, which in some cases (e.g., straight contours) could be quite
distant from the desired location.

This centers the label on  the closest point on contour itself (using
linear interpolation between vertices).
pep-8 compliance for commit 283f358
pep-8 compliance for rest of contour.py
mention contour plot label positioning in whats_new.rst
add simple test for contour label positioning
remove uneeded files
Make default arrow head width sensible

Currently the default head width is too small to produce a visible arrow
head by default, so make it bigger.
Update api change to reflect new default
added figure.frameon and savefig.frameon to rcparams
use """ everywhere instead of '''
use np.inf instead of arbitrary 1e10
better doc as suggested.
Fix bug where basedirlist was treated as a single string
Strip each entry of basedirlist
Merge pull request #1865 from rephorm/contour_label_pos

Fix manual contour label positions on sparse contours
Merge pull request #1875 from Tillsten/add_frameon_rc

[EHN] Add frameon and savefig.frameon to rcParams
Merge pull request #1186 from dmcdougall/arrow

Make default arrowhead width more sensible
Merge pull request #1874 from mdboom/basedirlist-bug

fix reading basedirlist from setup.cfg