Add TextureHints font metric.

By default, load fonts as 4-bit grayscale, 4-bit alpha (I4A4) maps.
This halves font texture memory usage.

stepmania/src/Font.cpp

@@ -39,7 +39,14 @@ void FontPage::Load( FontPageSettings cfg )
 
 	// load texture
 	RageTextureID ID(m_sTexturePath);
-	ID.iColorDepth = 16;
+	if( cfg.TextureHints != "default" )
+		ID.AdditionalTextureHints = cfg.TextureHints;
+	else
+	{
+		/* Using grayscale and 16bpp together means to use a 16bpp image if a grayscale 
+		 * image couldn't be loaded. */
+		ID.AdditionalTextureHints = "grayscale 16bpp";
+	}
 
 	m_pTexture = TEXTUREMAN->LoadTexture( ID );
 	ASSERT( m_pTexture != NULL );
@@ -484,6 +491,7 @@ void Font::LoadFontPageSettings(FontPageSettings &cfg, IniFile &ini, const CStri
 	ini.GetValue( PageName, "Baseline", cfg.Baseline );
 	ini.GetValue( PageName, "DefaultWidth", cfg.DefaultWidth );
 	ini.GetValue( PageName, "AdvanceExtraPixels", cfg.AdvanceExtraPixels );
+	ini.GetValue( PageName, "TextureHints", cfg.TextureHints );
 
 	/* Iterate over all keys. */
 	const IniFile::key *k = ini.GetKey(PageName);

stepmania/src/Font.h

@@ -48,7 +48,8 @@ struct FontPageSettings
 		DefaultWidth,
 		AdvanceExtraPixels;
 	float ScaleAllWidthsBy;
-	
+	CString TextureHints;
+
 	map<longchar,int> CharToGlyphNo;
 	/* If a value is missing, the width of the texture frame is used. */
 	map<int,int> GlyphWidths;
@@ -61,7 +62,8 @@ struct FontPageSettings
 		Baseline(-1),
 		DefaultWidth(-1),
 		AdvanceExtraPixels(1),
-		ScaleAllWidthsBy(1)
+		ScaleAllWidthsBy(1),
+		TextureHints("default")
 	{ }
 
 	/* Map a range from a character map to glyphs.  If cnt is -1, map the