DOC : add link to `plt.subplots` from `Figure.add_subplot`
Merge pull request #2847 from tacaswell/subplot_doc

DOC : add link to `plt.subplots` from `Figure.add_subplot`
Fixed issues with errorbar limits
Condensed setting values in lines_kw and plot_kw in the errorbar function
added errorbar limit test
added comments; fixed typo
removed extra space; pep8
fixes direction of arrowhead plot symbol for inverted x or y axes
updated api_changes and whats_new
removed rebase marker in test_axes