Add density parameter for correct handling density on vectorial images ....

[niwinz]

like pdf, svg, etc.

Is same code that #28
As the original author has said it will send the pull request, but has already spent two months since.

All credits to the original creator of the patch, I just need this functionality.

[dahlia]

Many things had changed (see #58 — it contains explicit read() method and resolution property which means density), so it should:

• contain tests for it
• not declare duplicate MagickSetImageResolution() signature (use Image.resolution property instead)
• rename density to resolution
• move the parameter from __init__() to read()

Thanks!

[niwinz]

Hello!
Having the property "resolution", my pull request ceases to have much meaning. But, I think the method is useful resolution, in method "init", besides read.

I will create another smaller pull request with these small changes.