add a self-contained text to image renderer
add a self-contained text to image renderer

This has an embedded font based on the IBM VGA font found in a
CC-licensed repo.

It can render arbitrary text using that font using Go's built-in
image library.

The first purpose is to be able to render text tables like the one
below and send them to Slack so they stay formatted for easy reading.
This is working and the code will follow in subsequent commits.

╔══════════╤═══════╤═════════╗
║ HEADER 1 │ HDR 2 │ LOL WUT ║
╟──────────┼───────┼─────────╢
║      one │   two │   three ║
║     four │  five │     six ║
╚══════════╧═══════╧═════════╝

Netflix/hal-9001