Text Rendering / Clarity: Investigate subpixel rendering strategies

[bryphe]

Issue: On Low DPI displays, the text rendering is not as clear as it could be.

One common technique for dealing with this is subpixel rendering, which exploits the fact that LGB displays tend to have strips in RGB order.

It's a strategy for increasing the resolution of font rendering by taking advantage of this pixel geometry.

@cryza did some amazing work in Oni to set up a full-WebGL based subpixel rendering strategy: onivim/oni#2120

The idea, as I understand it, was to render the same glyph 4 times (for each subpixel offset case), and then pick the appropriate one based on the pixel offset of the actual glyph. It would be great to have a similar strategy here, in combination with #108 - we'd have some really sharp font rendering 😄

[bryphe]

This is here with #567 !

Huge improvement in text clarity on low-DPI displays.