Fixed some errors in the README and improved comments in petscrc
Fixed OpenCL stats not displaying correct values when profiling is off
Added Cirrus build instructions
Removed OpenCL in Makefile (performance is worse with it enabled) and improved printing when using >1 process
Fixed Makefile to specify to use python3
Fixed mistake in Makefile, and added some ifdefs for the GPU code
-Added convergence test for OpenCL pressure solver
Moved all GPU options into petscrc, streamlined GPU's C wrappers