Merge branch 'master' into docking

# Conflicts:
#	docs/CHANGELOG.txt
#	imgui.cpp

docs/TODO.txt

@@ -354,6 +354,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - nav: some features such as PageUp/Down/Home/End should probably work without ImGuiConfigFlags_NavEnableKeyboard? (where do we draw the line?)
  - nav: configuration flag to disable global shortcuts (currently only CTRL-Tab) ?
  ! nav: never clear NavId on some setup (e.g. gamepad centric)
+ - nav: scroll up/down if possible when move request fails
  - nav: there's currently no way to completely clear focus with the keyboard. depending on patterns used by the application to dispatch inputs, it may be desirable.
  - nav: code to focus child-window on restoring NavId appears to have issue: e.g. when focus change is implicit because of window closure.
  - nav: Home/End behavior when navigable item is not fully visible at the edge of scrolling? should be backtrack to keep item into view?
@@ -381,8 +382,6 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - nav/windowing: when CTRL-Tab/windowing is active, the HoveredWindow detection doesn't take account of the window display re-ordering.
  - nav/windowing: Resizing window will currently fail with certain types of resizing constraints/callback applied
  - focus: preserve ActiveId/focus stack state, e.g. when opening a menu and close it, previously selected InputText() focus gets restored (#622)
- - focus: SetKeyboardFocusHere() on with >= 0 offset could be done on same frame (else latch and modulate on beginning of next frame)
- - focus: unable to use SetKeyboardFocusHere() on clipped widgets. (#787, #343)
 
  - viewport: make it possible to have no main/hosting viewport
  - viewport: We set ImGuiViewportFlags_NoFocusOnAppearing in a way that is required for GLFW/SDL binding, but could be handled better without