Fonts: automatically set current rasterizer density to viewport density. Effectively should fix most things on macOS.

# Conflicts:
#	imgui.cpp
#	imgui.h

docs/FONTS.md

@@ -130,7 +130,7 @@ ImGui::PopFont();
 **For advanced options create a ImFontConfig structure and pass it to the AddFont() function (it will be copied internally):**
 ```cpp
 ImFontConfig config;
-config.RasterizerDensity = 2.0f;
+config.OversampleH = 1.0f;
 ImFont* font = io.Fonts->AddFontFromFileTTF("font.ttf", size_pixels, &config);
 ```