v0.4.0

ClimaComms v0.4.0

Diff since v0.3.5

Closed issues:

• Automatically determine which comms context to use (#38)
• MPI persistent=false is broken (#41)

Merged pull requests:

• Simplify ClimaComms (#40) (@simonbyrne)
• Fix bug effecting non-persistent MPI communication (#42) (@sriharshakandala)
• Add compat entry for MPI. (#44) (@sriharshakandala)