Add new energy grid search based on an equal log-spaced mapping technique as
outlined in LA-UR-14-24530.
Change logarithmic energy grid to default.
Update documentation for <energy_grid>.
Merge branch 'develop' into log-energy-grid
Merge branch 'develop' into log-energy-grid
Merge branch 'develop' into log-energy-grid

Conflicts:
	src/input_xml.F90
Remove union energy grid treatment.
Merge branch 'develop' into log-energy-grid
Update documentation to reflect no use of union energy grid.
Fix headings in cross section documentation.
Add new evaporation spectrum sampling method outlined in LA-UR-14-27694. Still
need documentation.
Update documentation for evaporation spectrum.
Change !$omp critical directives to !$omp atomic where possible.
Make global_tallies allocatable instead of automatic.
Merge branch 'develop' into atomic
Merge pull request #342 from paulromano/atomic

Use OpenMP atomic updates instead of critical sections
Mention CMake in quick install instructions.
Merge pull request #337 from paulromano/evaporation

Improved evaporation spectrum sampling algorithm
Merge branch 'develop' into log-energy-grid
Make number of bins for log grid adjustable by user.