Make font atlas packing padding configurable

imgui.h

@@ -1382,6 +1382,7 @@ struct ImFontAtlas
     int                         TexWidth;           // Texture width calculated during Build().
     int                         TexHeight;          // Texture height calculated during Build().
     int                         TexDesiredWidth;    // Texture width desired by user before Build(). Must be a power-of-two. If have many glyphs your graphics API have texture size restrictions you may want to increase texture width to decrease height.
+	int                         TexGlyphPadding;    // Padding between glyphs within texture in pixels. Defaults to 1.
     ImVec2                      TexUvWhitePixel;    // Texture coordinates to a white pixel
     ImVector<ImFont*>           Fonts;              // Hold all the fonts returned by AddFont*. Fonts[0] is the default font upon calling ImGui::NewFrame(), use ImGui::PushFont()/PopFont() to change the current font.