fix unused variable warning by clang

Renamed ImDrawList::AddArc() to ImDrawList::AddArcFast() for compatibility with future API, and changed 2*PI range from 0..12 to 0..16

Fixed IsRootWindowOrAnyChildFocused() crashing if no window has focus (introduced yesterday in c38c54a)

Fixed user-facing version of IsItemHovered() ignoring overlapping windows

Added ShowMetricsWindow()

Added (not exposed) DisableHideTextAfterDoubleHash to disable ## processing.

Added IO.MetricsVertices counter

Examples: Fixed ShowExampleAppManipulatingWindowTitle() not doing the right thing, broken in ff35d24

Clicking on void loses keyboard-focus so application can use TAB back

Allow SetWindowFocus(NULL) to remove focus

DragFloat() comment examples, not ready for prime-time #180

DragFloat() examples #180

DragFloat() double-clicking turns into an input box (along with Ctrl+clicking) #180

DragFloat(): passing min>=max (e.g. 0.0f) for range makes the drag unbound #180, removed extra APIs

SliderFloat() removed support for unbound/infinite slider, inconsistent. Use InputFloat()/DragFloat()

Selectable() render into AutoFitPadding but do not extend it, fixing small visual gap ...

Followup 2e26196 /  #1

Combo() adding frame padding inside the combo box.

InputInt2(), InputInt3(), InputInt4(): fixed label vertical alignment

ShowTestWindow() renamed sliders examples to say "slider"

Added DragFloat(), DragInt() work in progress #180

ColorEdit4(): tweak code to be a little less ugly (still not a beauty contest winner..)

ColorEdit4(): hide components prefix if there's no space for them.

Comments and organization of imgui.h

Slider: don't call RenderText() on empty label.

Slider: fix in the unlikely case that style.GrabMinSize is larger than a slider.

Internal renaming

Delete font clear pointer in ImGui state to get a clear crasah instead of a dangling pointer. #181

Fixed Begin() returning true on collapsed windows that loaded settings #176

Fix uninitialized fields - MouseCursor set by first call to NewFrame()

Fix for Coverity static analysis