Updated release notes for 0.5.4.
bumped version to 0.5.4
Fixed p_valid sampling of energy distributions.
Updated test results for three tests.

The prompt neutron energy distribution for Pu-240 second-chance fission (MT=20)
was affected by the bug in #249 for three tests.
Merge pull request #250 from nelsonag/p_valid

Fixed p_valid sampling
Fix typo 'indicies' affecting CMFD data in statepoint.
removed filename from message, path_source_point instead
if user wants overwrite latest, source must be separate
fixed memory leak particle during sample external source sites
Fix out-of-bounds error when using OpenMP threading. Closes #255 on github.
Updated installation instructions.
Merge pull request #224 from mit-crpg/cmake

Transition build system to CMake
source present should only be written by master
Updated release notes with one more bug fix.
set default cmfd display to rms balance
updated statepoint revision documentation
added default value to overwrite latest
Merge branch 'release-v0.5.4'
Merge branch 'release-v0.5.4' into develop
Merge branch 'master' into develop