WIP: make source code builder more generic.
Importing some tools from previous branch.
Added lmdb to prerequisite fetch.
Work on expanding scons build system.
scons now has support for building DB as a library, and creating tests.
Added a script to run tests, fixed link ordering, use static LMDB only.
Modernize source: move from NULL to nullptr.
Move from boost unordered map to standard unordered map.
Revert unintended rename of VAL_
put boost::unordered_map back in temporarily until the hash functions are put in place