DOC : improved `extent` of `imshow` doc

closes #990
slight edits to docs as suggested by @mdboom
Use 'y#' instead of 's#' in write_rgba of the agg backend. Fixes #1891.
Merge pull request #2739 from tacaswell/extent_doc

DOC : improved `extent` of `imshow` doc
Removed 'ipython -pylab' references
Removed references to notebook
Merge pull request #3007 from cgardn/issue3005

#3005 - Removed 'ipython -pylab' references
Prevent mpl_PyFile_Dup from failing when given BytesIO or similar
Merge pull request #2898 from bytbox/v1.3.x

Fix animation errors
Merge remote-tracking branch 'upstream/v1.3.x'

Conflicts:
	CHANGELOG