Added aggregation support to MPI_NRM library. It uses the modified
downstream API to transmit compute and total time of a phase.

The NRM damper value is used for aggregation, and phases smaller than
this value are aggregated. The _aggregation parameter keeps track of
the number of phases that are aggregated for the total time to be
greater than the damper value.

See Issue #2

Removed all the measurement capability as it will be handled by the NRM.
Also, update Makefile and README to reflect this change

See Issue #1