Warning fix. (#1565)

Updated version to 1.60 WIP to emphasis on the addition of required calls CreateContext/DestroyContext + merged the massive Navigation branch (#1565, #787)

Merge branch 'context' ...

# Conflicts:
#	examples/allegro5_example/main.cpp
#	examples/directx10_example/main.cpp
#	examples/directx11_example/main.cpp
#	examples/directx9_example/main.cpp
#	examples/marmalade_example/main.cpp
#	examples/opengl2_example/main.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/vulkan_example/main.cpp

Nav: Documentation tweaks. (#787)

Nav: Keyboard is now automatically mapped based on io.KeyDown[]. (#787)

Nav: Toward automatically mapping keyboard input. Renamed ImGuiNavInput_PadXXX to ImGuiNavInput_XXX. Renamed ImGuiNavInput_KeyXXX to ImGuiNavInput_KeyXXX_ (internal). (#787)

Nav: Comments, guides.

Merge branch 'master' into context

Merge branch 'master' into navigation ...

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

Drag and Drop: TreeNode as drop target displays rectangle over full frame. Added optional internal storage for item display rect. Will expose later. (#1597, #143)

Internals: TreeNode: Renaming local to be more consistent with other widgets.

Internals: Refactored bool LastItemRectHovered into flags. (#1597)

Nav: Comments, removed extraneous parameter.

Nav: SetItemDefaultFocus() doesn't make the navigation cursorr highlight visible. Renamed NavInitResultExplicit to NavInitRequestFromMove. (#787)

Nav: Sliders and Drags are toggle activated instead of requiring user to cross Cross/Space. (#787)

Nav: DragBehavior: Tweaks (to take the noise out of the next commit).

Nav: Maintaining a NavActivatePressedId field that widget can conveniently use along with NavActivateDownId.

Nav: Removed old unnecessary ifdefs.

Nav: Debugging code. (#787)

Nav: Sets io.WantCaptureKeyboard when navigation is active. This is a little agressive but probably the best default and also a good way to get feedback. Added ImGuiNavFlags_NoCaptureKeyboard to disable this behavior. Comments. (#787)

Merge branch 'master' into navigation ...

# Conflicts:
#	imgui.cpp

Tooltip: BeginTooltip() sets NoInputs flag.

Style: Fixed missing style.MouseCursorScale initialization (#939), messed up original commit badly.

Merge branch 'master' into navigation ...

# Conflicts:
#	imgui.cpp

Nav: Minor tidying up. (#787)

Merging the minor/shallow changes from Navigation branch.

Added assert in BeginChild(ImGuiId id).

Nav: Debugging stuff.

Nav: Ensure g.NavScoringRectScreen is always finite and not inverted. (#787)

Merge branch 'master' into navigation ...

# Conflicts:
#	imgui.cpp