Use make -j2 for compiling

Nowadays processors generally have 2 threads or more available, whether that is a single core CPU with 2 threads, or a dual core computer with 1 thread each. Make on 1 thread is very unbearably slow, especially when on an 8 core computer.
So I propose that this gets changed to make -j2 so it is faster on computers with the extra threads, and doesn't have much of an effect on those who do not have more than 1 thread.