Fixes, new command and build.cmd

- fixed a bug in ScriptPack::Terminate where the logic wouldn't null out
the ClrMdPack instance if it wasn't attached
- changed DumpFinalizerQueueHeapStatsByType(minSize) from int to long
- added DumpStack command
- changed ConsoleOutputWriter::WriteLineSeparator to write only half the
console width for aesthetics
- added a build.cmd file to support easy building without having to fire
up Visual Studio