implement effhist and helper function
implement tests for effhist
changes in response to comments in PR
changes in response to PR comments
implement wald interval
docstrings; test wald; rename binned_efficiency()
plot titles and wald interval discussion
added matplotlib to travis sphinx build

specific version selected because py 3.x build errors occur on released
version
build scipy with sphinx test so matplotlib extension works
go back to regular mpl b/c sphinx build not in 3.x
updated build order and clarified some comments
Merge pull request #754 from kbarbary/effhist (manual merge) travis test fixes also included from eteq/effhist