Add option to draw_ulh to draw difference between data and PDF
Add option to draw_blh to draw difference between data and PDF
Merge upstream
add analytical integral to HistogramPdf
Merge with upstream
Fix draw_blh
Fix draw_blh normalization.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	probfit/_libstat.c
	probfit/costfunc.c
	probfit/functor.c
	probfit/funcutil.c
	probfit/pdf.c
Remove some comments
Separate draw_diff option from draw_ulh() and draw_blh() to separate functions draw_residual_ulh() and draw_residual_blh()
Change default draw/draw_residual of UnbinnedLH to plot points with errorbars. Add tests to testplotting.py.
Add integrate test of HistogramPdf. Change default of draw_residual to not showing parameters.
Merge pull request #33 from gitcheng/master

Options in draw_ulh, draw_blh; analytical integral of HistogramPdf