vinyl: implement space.bsize, index.bsize, and index.len

 - space.bsize returns the size of user data stored in the space.
   It is the sum of memory.bytes and disk.bytes as reported by
   the primary index.

 - index.bsize returns the size of memory used for indexing data.
   It is the sum of memory.index_size, disk.index_size, and
   disk.bloom_size as reported by index.info. For secondary indexes
   we also add the size of binary data stored on disk (disk.bytes),
   because it is only needed to build the index.

 - index.len returns the total number of rows stored in the index.
   It is the sum of memory.rows and disk.rows as reported by
   index.info. Note, it may be greater than the number of tuples
   stored in the space, because it includes DELETE and UPDATE
   statements.

Closes #2863
Closes #3056