Ensure that binary series constructed from blocks are distinct

When passed a block argument, `make_binary` populates and returns a
pointer to a temporary buffer in the task context.  As a result,
binary series constructed from block specs are subject to unexpected
mutation:

    >> x: to binary! [1]
    == #{01}
    >> y: to binary! [2]
    == #{02}
    >> x
    == #{02}
    >> same? to binary! [1] to binary! [2]
    == true

Correct this behaviour by returning a copy of the constructed series.
Merge pull request #106 from 0branch/block-to-binary

Ensure that binary series constructed from blocks are distinct (whoops, good one -cs)