Support asymmetric density

[tresf]

Currently, when specifying density (e.g. { density: 300 }) QZ Tray will create a resolution of 300x300. However some printers, such as the Dymo Labelwriter 450 support a resolution of 300x600.

By leveraging the Windows print driver, it's possible to obtain this higher quality...

Note, this does slow printing considerably, but the output is undeniably better.

I would like to propose the following:

• The ability for density to allow asymmetric density values
• The ability for density to be triggered by qualitative keywords, e.g. "Best".

[akberenz]

How do we want to go about supporting this in the api?

• Take an array for [cross, feed] densities
  • { density: [300, 600] }
• Take an object with cross and feed as the key names
  • { density: { cross: 300, feed: 600 } }
• Add an additional config property for cross density, leaving 'density' as feed density
  • { crossDensity: 300, density: 600 }

And I'm assuming "best" would just go for the highest supported values of both? Are there other string keywords we'd want to support?

[tresf]

2. { density: { cross: 300, feed: 600 } }

^--- This is the winner. I'll explain why...

1. { density: [300, 600] }

This allows an array already, so it's used up already.

3. { crossDensity: 300, density: 600 }

I think density: { density: ... } } is confusing.

And I'm assuming "best" would just go for the highest supported values of both?

Yes.

Are there other string keywords we'd want to support.

The most common I'm finding are:

• BEST
• NORMAL
• DRAFT

We can probably infer BEST and DRAFT by choosing the highest and lowest values respectively, but I have no idea how to compute NORMAL. Since most drivers will ship with NORMAL as the default, perhaps we just support the prior and latter for now and then we can do a separate study at a later time (not in this PR) titled:

Issue #999: "what is NORMAL" density
Placeholder to sample a handful of drivers on various platforms to determine if there's a programmatic way to support NORMAL.

Even then, it may not be needed, most programmers know the DPI of their printer.