use a vtable approach for generic map interface
drwxr-xr-x - include
-rw-r--r-- 1905 license.txt
-rw-r--r-- 3236 makefile
drwxr-xr-x - map
drwxr-xr-x - runtime
drwxr-xr-x - test
-rw-r--r-- 482 todo
drwxr-xr-x - txn