* igCollapsingHeader (3-params) renamed to igCollapsingHeaderEx.
* igColor and igColor2 removed -- they no longer exist in cimgui.
* igBeginMenu (1-param) removed. igBegin is already imported, and it has
two parameters, not one.
* Fixed two typos in DrawList function names.
* Font -> NativeFont. Font is now a wrapper class for the NativeFont
struct.
* FontAtlasWrapped -> FontAtlas, and FontAtlas -> NativeFontAtlas, in line
with other native struct wrappers.
* [BREAKING CHANGE] Removed ImGui.LoadDefaultFont(). It is now available on FontAtlas along
with other Font loading methods. This makes more sense w.r.t. the actual
native interface.
* Modified the SampleProgram to account for the above.
* New wrapper: ImGui.SetKeyboardFocusHere([int offset])
A lot of random things, also added some popups to the demo
program to test them, etc. Wrote some additional wrappers for
existing methods to better support optional/default parameters
in the original C++ API.