Add isend, iprobe, iprobe_recv, test
Update test cases to use nothing instead of Nothing
Ignore file
Return boolean flag from iprobe_recv
Add more MPI constants; rewrite code
Add isend/irecv; rewrite code
Update tests
Update documentation
Use Int instead of Int32 for process ids
Correct install directory
Use Cint instead of Int32
Merge pull request #16 from eschnett/master

Implement irecv