Merge pull request #16 from gitcheng/master

Add a pdf class HistogramPdf
fix #18
Merge pull request #19 from piti118/fix18

fix #18
add nint_subdiv to control how binned chi^2 and binned LH calculate
expected number of event
fix the failed test
Merge pull request #21 from piti118/better_integral_binlh

add nint_subdiv to control how binned chi^2 and binned LH calculate expected number of event
clean up doc
Merge pull request #22 from piti118/better_integral_binlh

clean up doc
Add option show_errbars to draw_ulh so one can show error bars in data. Add *~ to .gitingore.
merge with upstream
Add back the files that aren't supposed to be untracked.
Use Simpson's rule in  integrate1d_with_edges.