Update fontgen to output D instead of C

Rsconscript

@@ -71,9 +71,14 @@ fontgen_env = env "fontgen", use: "freetype" do |env|
 end
 
 hulk_env = env "hulk", use: %w[ldc2 x86_64-elf-gcc] do |env|
+  env.add_builder(FontGen)
+  env.FontGen("^/src/hulk/kfont.d", "font/Hack-Regular.ttf",
+              "fontgen" => fontgen_env.expand("^/fontgen"))
   env["sources"] = glob("src/hulk/**/*.d")
+  env["sources"] << "^/src/hulk/kfont.d"
   env["DFLAGS"] += %w[-mtriple=x86_64-unknown-elf --betterC -release -O3 --wi --enable-cross-module-inlining]
   env["D_IMPORT_PATH"] += %w[src]
+  env["D_IMPORT_PATH"] << env.expand("^/src")
   env["LD"] = "x86_64-elf-gcc"
   env["LDFLAGS"] += %w[-nostdlib -Tsrc/hulk/hulk.ld -Wl,-Map,${_TARGET}.map]
   env["LDCMD"] = %w[${LD} -o ${_TARGET} ${LDFLAGS} ${_SOURCES} ${LIBDIRPREFIX}${LIBPATH} ${LIBLINKPREFIX}${LIBS}]