Limited localisation support when encoding environment

The game appears to be using latin-1 / ISO-8859-1/2 or something
similar (I'll need to test various characters to determine exactly
which) for in-game text. Treat the JSON file as latin-1 encoded and pass
these through to the game.
Add GIMP Scripts to help with localising textures
More GIMP Scripts to help remove text for localisation

These need mask images, which I haven't committed due to their size.
They were generated by combining all the images using the same
background in lighten only mode in the GIMP to eliminate text and
distinct images (and some manual cloning for common text, etc).

Once the mask is applied to the images they still need manual editing in
the GIMP to show wanted parts (images, etc) of the source image through.
Miasmata is using Windows 1252, so use cp1252 instead of latin-1
Fix another localisation issue
Allow JSON encoded environment diffs to be produced encoded in utf-8

On the one hand I could have encoded the miasmod diffs in cp1252 to
match what the game uses, but I think that more text editors will
default to utf-8, and I can't figure out the proper incantation to get
vim to treat the file as encoded in cp1252, so... utf-8 it is.
data.py: Don't print diff with --apply-diff
Add script to generate intro slides
Try a newer version of the file-dds-save plugin API
French translation by Alexandre Conte