plothist(x) now uses hist(x), fix ticks on x

Histogram on Winston.jl set x0 to 0 by default (have a fix me comment) and I don't know how to fix it.
For fix it on plothist(), I subtract the start of the range to ticks (in order to start on 0), but I use the range for labels in order to get the desired output.
Works fine, except when the number of bins is too large (labels superpose between them, but can be fixed by user setting a nbins to a lower number for example).
Merge pull request #67 from diegozea/patch-1

plothist(x) now uses hist(x), fix ticks on x