First attempt at modelling image device pixel ratio based on the @dprx notation
Removed unused path reference
Reuse Asset.prototype.fileName getter/setter where possible
Stricten device pixel ratio setter to only allow number types
Stricten device pixel ratio setter to disallow 0, Infinity, negative numbers and filename unfriendly notations
Test assets/Image fileName and device pixel ratio getter/setter
Changed device pixel ratio interface to not change filename as a side effect ever
Test that changes in filename only affects device pixel ratio if the special syntax is part of the new name
Merge pull request #233 from assetgraph/device-pixel-ratio

Model image device pixel ratio