Extract grid dashing.
Extract field access helpers from DSL.
New outside clue parsing helpers.

Can now parse integers from
  left: [1,35,-,4444]
Backend context alias.
Non-Maybe grid for fillomino solution
Use `pointDiagram` instead of `vrule 0`.
Borders for fillomino solution
Add grid char replacement parser.

Can now parse a grid of integers from

both

puzzle: |
  123
  234
  345

and

puzzle:
  grid: |
    12a
	a34
	3bb
  replace:
    a: 100
	b: 5
Extended grid parsing for fillomino solutions.
Slightly expand background shading squares.

They used to go exactly to the grid lines, which is half a pixel
in .png, leading to artifacts when not covered by lines. Now
includes the grid lines, which could cause unevenness if we on
tile borders without grid lines, but we might be able to avoid
those.
Fix japanese sum solution rendering by putting shaded cells on bottom.
Get grid cells from the map keys.

Supports irregular grids.
Calculating borders for irregular grids.
Irregular area grids (with blackened cells)
Wider lines for solutions.
Port Either' back to FromChar...
Kill unused import.