ImVector: Added index_from_pointer() helper.
ImVector: Added index_from_pointer() helper.

burningreggae/imgui,burningreggae/imgui,ggtucker/imgui,aimotive/imgui-glfw,dougbinks/imgui,Flix01/imgui,cmaughan/imgui,ocornut/imgui,Flix01/imgui,ocornut/imgui,nProtect/imgui,bkaradzic/imgui,bkaradzic/imgui,aimotive/imgui-glfw,ggtucker/imgui,dougbinks/imgui,ocornut/imgui,nProtect/imgui,wflohry/imgui-addons,cmaughan/imgui,Flix01/imgui,wflohry/imgui-addons,bkaradzic/imgui,cmaughan/imgui,ggtucker/imgui,nProtect/imgui,cmaughan/imgui