Append _ 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.

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.