translate ! to not_ in Cut.safe()
Merge pull request #555 from ndawe/master

[MRG] translate ! to not_ in Cut.safe()
add TArrow
return the axes bounds from utils.draw
Merge pull request #556 from ndawe/master

[MRG] add TArrow
Merge pull request #557 from ndawe/master

[MRG] return the axes bounds from utils.draw
ratioplot template
add fill_value argument to Hist.divide
RatioPlot: set tick lengths
RatioPlot: draw horizontal lines in ratio pad
_limits_helper: don't raise ValueError and instead return reasonable values if min=max
templates: center ratio plot y-axis title