Added missing IMGUI_API definitions in imgui_internal (fix #326)
Added missing IMGUI_API definitions in imgui_internal (fix #326)

bkaradzic/imgui,cmaughan/imgui,aimotive/imgui-glfw,elect86/imgui,thevaber/imgui,mikesart/imgui,ocornut/imgui,dougbinks/imgui,rxantos/imgui,Flix01/imgui,emoon/imgui,wflohry/imgui-addons,Pagghiu/imgui,wflohry/imgui-addons,nProtect/imgui,neshume/imgui,nProtect/imgui,rxantos/imgui,emoon/imgui,elect86/imgui,ggtucker/imgui,burningreggae/imgui,nmlgc/imgui,thennequin/imgui,redblobgames/imgui,Flix01/imgui,Psybrus/imgui,bkaradzic/imgui,burningreggae/imgui,ggtucker/imgui,zho7611/imgui,Flix01/imgui,Psybrus/imgui,tom-seddon/imgui,kylawl/imgui,aimotive/imgui-glfw,neshume/imgui,zho7611/imgui,thevaber/imgui,bkaradzic/imgui,tom-seddon/imgui,seanmiddleditch/imgui,nProtect/imgui,cmaughan/imgui,nmlgc/imgui,thennequin/imgui,mikesart/imgui,Pagghiu/imgui,usagi/imguixx,usagi/imguixx,ggtucker/imgui,dougbinks/imgui,wasikuss/imgui,cmaughan/imgui,cmaughan/imgui,seanmiddleditch/imgui,ocornut/imgui,kylawl/imgui,wasikuss/imgui,redblobgames/imgui,ocornut/imgui