Updated file format so that aligning to disk sectors is easier/possible, and added field to specify ciphersuite.  Updated code to reflect this.  Updated API so that an MDB struct is passed to all functions, instead of using global state.  Various code cleanups.  Added more information to file format specification file, and cleaned up formatting.
Bug fixes.
Cleaned up meagerdb.h header.
mdb_create will no longer overwrite existing files.
BUG: mdb_insert_finalize did not check if database was open.
BUG: mdb_select_by_page did not return MDBE_NOT_OPEN when the database was closed.