Replace EFPs and FNTs with PNGs

[akx]

This PR:

• adds Python conversion tooling for EFP -> PNG and FNT -> PNG
• replaces the Error Free Picture (EFP) assets with PNGs and replaces the loading code to look for "FOO.png" when "FOO.EFP" is requested.
• replaces the FNT assets with PNGs and replaces the loading and drawing code with something somewhat saner. The original code was hard enough to make sense of.

The game code itself (call sites to EFP loading and text drawing) remains unmodified.

Fixes #115
Fixes #118

[veikkos]

Readme has libraries section and Windows specific cmake spell, which should be updated to include SDL_image.

[veikkos]

Could consider putting new files under still existing SRC/EFP directory as SRC directory has lots of files. Which reminds me that I should have actually done that with some new files introduced lately. Need to craft a PR.

[akx]

Could consider putting new files under still existing SRC/EFP directory as SRC directory has lots of files.

I disagree, since we're getting rid of EFPs as a concept here.

[akx]

@veikkos Ready for re-review.

[veikkos]

Would have renamed .EFP -> .PNG instead of .png like rest of the files. :-)

[akx]

Would have renamed .EFP -> .PNG instead of .png like rest of the files. :-)

Sure. Added a commit to do that.

Aside: it makes perfect sense really, but on a case-insensitive file system like my Mac's APFS, one needs to git rm --cached ...; git add files for Git to pick up the case changes.