Basic unit support

Basic unit conversion from pt, pc, cm, mm, in to px.
going to fix, i double checked but those spaces always comes out. please
get an eye even on the other pr.

for visual effects of this commit check asset 73 the building plant drawn
in ligth blue. now the stroke has the correct width from 0.5px to 0.5mm in
pixels :)

for the changable dpi i read somewhere that in css styling they should be
considered alwayas 96px per inch. cannot remember if it was on mdn or
generic article on internet. having it external won't hurt anyway.
Il 16/lug/2014 19:25 "Stefan Kienzle" <notifications@github.com> ha scritto:

> In src/util/misc.js:
>
> > @@ -132,6 +132,31 @@
> >        return parseFloat(Number(number).toFixed(fractionDigits));
> >      },
> >
> > +    parseUnit: function(value) {
> > +      var DPI = 96;
> > +      var unit = /\D{0,2}$/.exec(value);
> > +      var number = parseFloat(value.slice(0,-unit[0].length));
>
> Combine these var statements.
>
> —
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> <https://github.com/kangax/fabric.js/pull/1491/files#r15013886>.
>