ranges (#435).

* New`label_date_short(leading)` argument to replace leading zeroes (#442)

*`breaks_pretty()` will return the input limit when it has no range (#446)

*`transform_exp()` nowhas more sensible breaks, available in`breaks_exp()`

*`breaks_exp()` nowprovides more sensible breaks for the exponential transform

(@teunbrand,#405).

* The scales package now keeps track of known palettes. These can be retrieved

using`get_palette()` or registered using`set_palette()` (#396).

function(x)base^x,

function(x) log(x,base=base),

d_transform=function(x)base^x* log(base),

d_inverse=function(x)1/x/ log(base),

breaks= breaks_exp(),

d_inverse=function(x)1/x/ log(base)

)

}