Interface MCAlite

[MinliLiao]

This pull request adds the interface to use MCAlite as the backend for MCA.
To build RAPTOR with MCAlite support, add -D__RAPTOR_MCALITE_SOURCE_DIR=path/to/MCAlite/src to the cmake command when building RAPTOR.
MCAlite requires linkage to the math library, so -lm linkage option would need to be added when compiling application code with RAPTOR with MCAlite support.

Set the second parameter of __raptor_mca_op_func to 1 to use MCAlite. MCAlite does not use any of the last 3 truncate to parameters, so any valid value can be used, but they won't have any impact on the results.

The environment variables MCA_SEED, MCA_T, MCA_NTRIALS, MCA_MODE would set the random number generator seed rng_seed, virtual precision t, loop count of each operation ntrials and mca mode (RR, PB or FULL) mode respectively at runtime.
The default values are equivalent to MCA_SEED=42 MCA_T=24 MCA_NTRIALS=5 MCA_MODE=PB.

The statistics are calculated with mca_compute_stats function for each operation and aggregated and printed to stdout at the end of execution. Per operation statistic output can be silenced by setting MCA_QUIET environment variable to anything but empty.
No statistics are calculated when ntrials is 1 since the mca_compute_stats function would through errors.