Add more diacritics

[probonopd]

Add ÄÖÜäöü by using the diaeresis from Unicode characters 0401 and 0451.
As per fontforge/fontforge#283, follow the guide at http://designwithfontforge.com/en-US/Diacritics_and_Accents.html.

On a more general note, try to follow Context of Diacritics, which is an analysis of diacritics made to help type designers with refining the character sets of their fonts.

[probonopd]

http://designwithfontforge.com/en-US/Diacritics_and_Accents.html says:

So, using the example of building the ‘a acute’ character (u+00e1) , we would need to have already created the lowercase ‘a’ (u+0061) and the ‘acutecomb’ glyph (u+0301). Then selecting the ‘a acute’ character slot and using the ‘Element > Build > Build Accented Glyph’ function, FontForge will place a reference to the lowercase ‘a’ glyph and a reference to the ‘acutecomb’ glyph into the ‘a acute’ character slot (see below).

More information:
fontforge/fontforge#4304

[probonopd]

Possibly this could be done even more efficiently using RoboFab rather than FontForge. However, RoboFab seems to be replaced by https://github.com/robotools/fontParts. It the latter ready for prime time yet?

[probonopd]

For Diaeresis:

• Use diaeresis from U+0451, copy into U+0308 (without this it will not work at all)
• Prefereces -> Accents -> Set AccentOffsetPercent to 8 (this is a typographical property of this font)
• Press Ctrl-A to select all character slots (or a range of character slots, e.g., up to U+0100), and press Ctrl-Shift-A to build accented glyphs in all suitable character slots

https://www.youtube.com/watch?v=Mk9ShYmHJr8

[probonopd]

Diaeresis was added in db4819f.

[probonopd]

Key to doing this is to add Combining Diacritical Marks to the font as described in https://www.unicode.org/charts/PDF/U0300.pdf, then FontForge can automatically generate the combined characters.

For Accute:

• Use accute (spacing) from U+00B4, copy into U+0301 (without this it will not work at all)
• Prefereces -> Accents -> Set AccentOffsetPercent to 8 (this is a typographical property of this font)
• Press Ctrl-A to select all character slots (or a range of character slots, e.g., up to U+0100), and press Ctrl-Shift-A to build accented glyphs in all suitable character slots

For Circumflex:

• Use circumflex from U+005E), copy into U+0301 (without this it will not work at all)
• Prefereces -> Accents -> Set AccentOffsetPercent to 8 (this is a typographical property of this font)
• Press Ctrl-A to select all character slots (or a range of character slots, e.g., up to U+0100), and press Ctrl-Shift-A to build accented glyphs in all suitable character slots

For Grave:

• Use grave from U+0060 or U+FF40 (which one?), copy into U+0300 (without this it will not work at all)
• Prefereces -> Accents -> Set AccentOffsetPercent to 8 (this is a typographical property of this font)
• Press Ctrl-A to select all character slots (or a range of character slots, e.g., up to U+0100), and press Ctrl-Shift-A to build accented glyphs in all suitable character slots

For Cedilla:

• Use cedilla (spacing) from U+00B8, copy into U+0327 (without this it will not work at all)
• Prefereces -> Accents -> Set AccentOffsetPercent to 8 (this is a typographical property of this font)
• Press Ctrl-A to select all character slots (or a range of character slots, e.g., up to U+0100), and press Ctrl-Shift-A to build accented glyphs in all suitable character slots

For Tilde:

• Use tidle (spacing) from U+007E, copy into U+00303 (without this it will not work at all)
• Prefereces -> Accents -> Set AccentOffsetPercent to 8 (this is a typographical property of this font)
• Press Ctrl-A to select all character slots (or a range of character slots, e.g., up to U+0100), and press Ctrl-Shift-A to build accented glyphs in all suitable character slots