Branson 0.82, Parmetis removed

Release notes

• Dependency on ParMetis removed: root rank does the decomposition and broadcasts the results. This limits the size of problems that can be run (but ParMetis was failing when I was running with a billion cells anyway).
• CMake no longer looks for ParMetis and it's been removed from the overview.
• Slight change to buffer processing: ID's in use sets are cleared at the end of timestep to prevent some rarely seen errors in debug mode

Branson 0.81

There are no functional changes in the transport loop for Branson 0.81 from the last release except for a few casts to eliminate comparison warnings.
Changes:

• Use PUGI XML to parse XML input files instead of Boost XML reader
• Use a slightly smaller grip size in proxy_small to avoid running out of memory on trinitite nodes
• Remove Boost checks in the CMake
• Add a CI system for Github

Branson 0.8

This version of Branson has a few improvements to reduce memory use in the decomposition and the transport phase. It also uses a few RMA assertions to improve the speed of one-sided tally operations.

• Use a "Proto_Mesh" and "Proto_Cell" classes to do mesh decomposition and remapping with a lighter weight cell class. "Proto_Cell" does not have opacity, temperature or heat capacity and has about 80% less memory for the 50 group case
• Split off Proto_Mesh functions from standard Mesh functions.
• Statically size the census list during transport. "pushing back" was the main cause of memory growth beyond what was expected.
• Use more const references when returning received cell lists.
• Added a CMake build system.

The next release should have a working CI system and remove Boost dependency.

Release for SPACK build

This is a release to test building Branson automatically with SPACK (https://github.com/LLNL/spack).