Various scripts have diacritics on positions other than the top of base
characters. This commit adds support for the (optional) `placement` key
in diacritic.json, allowing diacritics to be placed in any of the four
positions: above, below, to the left, and to the right of the glyph.
The default when not specified is "above".
The placement respects the spacing specified by the `diacriticSpace`
key in characters.json.

This allows to define a glyph with multiple diacritics attached.
Currently overlaps are not handled (spacing is currently shared for
all of them), meaning stacking diacritics in the same direction is not
possible.

This adds various missing glyphs for Vietnamese.
Note that some characters require multiple diacritics in different positions.

There is a hack in diacritics.json to force monocraft.py to include many
glyphs in the generation step. For example, the glyph "LATIN SMALL LETTER
A WITH CIRCUMFLEX AND DOT BELOW" contain two diacritics `circumflex` and
`dot_below`. generate_diacritics.py parses this as containing one
diacritic: `circumflex_and_dot_below`, which it will not find in
diacritics.json without this hack, and thus the glyph will not be
generated.
For a proper fix, the logic to determine which diacritics should be
considered (lines 37-38, generate_diacritics.py) should be fixed to
consult the list in characters.json instead.

This commit adds support for two optional keys in diacritics.json: offsetX and offsetY. This allows the glyph to be shifted relative to the base position.

Some Vietnamese glyphs are very tall with their diacritics, which causes the top of them to sometimes be cut off in some programs. This raises the font ascent by 1 pixel size to accomodate those glyphs.
As a side effect, however, this also messes with font sizing in a lot of programs.

The original variant looks better in text, but is different from the
font in-game.

The original variant looks better in text, but is different from the
font in-game.

The last size bump did not take into account capital letters.