mpiP v3.1.1 release

We are pleased to announce the release of version 3.1.1 of the mpiP lightweight profiling library for MPI applications.

Release v3.1.1 addresses the following issues:

* Revert to gettimeofday as default Linux timer.
* MIPS64-Linux stack walking support.
* Catamount dclock timer support.
* Greater install flexibility:
o 'install' target only installs lib and doc files.
o 'install-api', 'install-bin', 'install-all' targets provide additional install functionality.
o New 'uninstall' target.