Added first pass of perf test of ht vs map.
Added first pass of perf test of ht vs map.

Does some simple timing on various forms of map access vs the hashtable.
$ ./dbcore-run dist/bin/test-hashtable -i -l 0 \
   --test map \
   --option writes 100000 \
   --option reads 100000

digitalbazaar/monarch,digitalbazaar/monarch,digitalbazaar/monarch,digitalbazaar/monarch,digitalbazaar/monarch