Style: Tweaked default border (undo half-way from original c1e1e015) (#707)

Renamed IsItemHoveredRect() to IsItemRectHovered(). Renamed IsMouseHoveringWindow() to IsWindowRectHovered() - follow up to previous commit 6be7d490  merged from Nav.

Style: Added obsolete redirects for ImGuiCol_Columns*** fields. (ref 648f75b2)

Merge part of 88c19666 from Nav branch. Renamed IsMouseHoveringAnyWindow() -> IsAnyWindowHovered(), IsMouseHoveringWindow() -> IsWindowHoveredRect() for consistency. Kept inline rediection function.

Merge 20a0fde0 Tidying up default clipboard handler for non Windows-OS (from Nav branch)

Merge 2545d75c from Nav - Tidying up, removed two unnecessary window flags from being exposed in imgui.h

Columns: Columns set resize based on the presence of vertical scrollbar. Not 100% sure about that but it looks like we've fixed enough bugs that this may not cause troubles anymore. (#125, #913, #893, #1138)

Columns: Fixed another form of shearing made visible by the PreserveWidth option. The code was initially added in c46d5634 to fix because we've fixed in e42aaede42eb6d8a47cf104f3afd6057b13a61ee. (#913, #125)

Columns: A set of column (and most importantly the right-most column) do not register its content to the parent, not affecting the window contents size. (#519, #125, #913)

Columns: Fixed one form of shearing during resizing columns with PreserveWidth enabled (there's another issue still). (#913, #125)

Columns: Removed unnecessary/misleading dummy ItemSize(). Was fixed already before, and fixed again in this branch by 3bf2af23. (#913, #125). End() calls EndColumns() directly.

Columns: Fixed offset rounding leading to SetColumnOffset() being destructive when ImGuiColumnsFlags_NoPreserveWidths flag is not set. (#913, #125)

Columns: Moved BeginColumns/EndColumns/flags from #913 to imgui_internals.h + minor shallow tweaks. Removed demo code temporarily. (#125)

# Conflicts:
#	imgui.cpp
#	imgui.h

Renamed GetStyleColName() to GetStyleColorName() for consistency. Extra comments in Api Breaking Changes section.

Scrollbar: Comments. Fixed potential div-by-zero error which I can repro now, so added an assert to notify us if it's actually ever useful or not.

ImFontAtlas::AddFontDefault: Made it possible to override size (even if it isn't really recommended)

Added PushStyleColor(ImGuiCol idx, ImU32 col) overload. (Which _might_ cause an "ambiguous call" compilation error if you are using ImColor() with implicit cast. Cast to ImU32 or ImVec4 explicily to fix.)