Append ' DLL' to DLL name to fix linker times

As reported in #72, the DLL having the same name as the EXE was causing long link times in Visual Studio. This commit renames the DLL to have an _ after the project name, fixing the link times. I should mention, @LuisAntonRebollo is responsible for this. I'm just requesting it officially...

Possibility: on load, the engine should look for DLLs with and without the underscore, so if you find it really obnoxious you can rename your DLL before shipping.