VIII.png: Fix several characters -- alignment & touch ups

* Fix character alignment of: '[', ']' and '\'.

Improve rendering of characters: 'b', 'a', 'o', 'p', 'r', 'K', 'M':

* Inner character space is now transparent -- area was previously
filled black.

* Trace over gray color spots with white -- this give us better
results when scaling up.
Update codebase to reflect latest nomlib API

  The following APIs within nomlib have changed:

* nom::BitmapFont
* nom::Gradient
* nom::Input
* nom::Label
* nom::SDL_App
src/Game.cpp: Refactor screenshot logic code

* We now let nomlib handle generating a unique identifier for our
output filename