Merge pull request #23 from gitcheng/master

Errorbar option in draw_ulh; Simpson's rule in integrate1d_with_edges
simpson3/8 and change default integral interval/faster test
update c file
Merge pull request #25 from piti118/better_integral_binlh

Simpsons3/8 integral and faster test
Add option to draw_ulh to draw difference between data and PDF
Add option to draw_blh to draw difference between data and PDF