Split sheet pages & shorten filenames

Now 256 sheets, 16x16 chars each (same as Minecraft), instead of one
huge sheet.

This greatly improves performance on initial texture loading (total
size also grows to ~2MB, though).

Filenames are now `unif_XX.png` (XX for codepoint's higher byte in hex
form).

README.md

@@ -7,7 +7,7 @@ This modpack provides mods with dynamic display. Mods are :
 - **[font_api](https://github.com/pyrollo/display_modpack/tree/master/font_api)**: A library for displaying fonts on entities;
 - **[signs_api](https://github.com/pyrollo/display_modpack/tree/master/signs_api)**: A library for the easy creation of signs;
 - **[font_metro](https://github.com/pyrollo/display_modpack/tree/master/font_metro)**: A font mod used as default font (includes uppercase, lowercase and accentuated latin letters, usual signs, cyrillic and greek letters)
-- **[unifont](https://github.com/pyrollo/display_modpack/tree/master/unifont)**: A lightweight (~1MB) font mod with full Unicode Plane 0 charset (63000+ chars)
+- **[unifont](https://github.com/pyrollo/display_modpack/tree/master/unifont)**: A lightweight (~2MB) font mod with full Unicode Plane 0 charset (63000+ chars)
 
 - **[boards](https://github.com/pyrollo/display_modpack/tree/master/boards)**: A mod providing school boards (includes *tiny cursive font*, a handwriting style font);
 - **[ontime_clocks](https://github.com/pyrollo/display_modpack/tree/master/ontime_clocks)**: A mod providing clocks which display the ingame time;

unifont/README.md

@@ -5,7 +5,7 @@
 GNU Unifont (v14.0.01) for Font API mod (from [display_modpack](https://github.com/pyrollo/display_modpack)).
 
 - Full Unicode Basic Multilingual Plane (BMP) with 63485 characters
-- Lightweight, only 1MB in size
+- Lightweight, data only ~2MB in size
 - Duospaced (glyphs in either 8x16 or 16x16)
 
 Requires `font_api` mod.

unifont/init.lua

@@ -34,9 +34,11 @@ local function get_glyph(codepoint)
 	if codepoint == 0 or codepoint > 0xffff or widths[codepoint] == nil then
 		codepoint = 0xfffd
 	end
-	local x = codepoint % 256
-	local y = math.floor(codepoint / 256)
-	return string.format("unifont_sheet.png^[sheet:256x256:%d,%d", x, y)
+	local page = math.floor(codepoint) / 256
+	local off = codepoint % 256
+	local x = off % 16
+	local y = math.floor(off / 16)
+	return string.format("unif_%02x.png^[sheet:16x16:%d,%d", page, x, y)
 end
 
 font_api.register_font(