Resolve TODO for `proc_grid_size`.

The constraint is now: ``proc_grid_size >= 1``.
Remove the TODO for block_size.

The constraint is still `block_size >= 1`.
Fix the constraint for when 'bc' == 'b'.

It's ceiling division, not floor division.
Resolve the cartesian-coordinates TODO.

Also add a link to the proper section of the MPI 2.2 standard (HTML version).
Add links to descriptions of the block-cyclic.

I vote for linking to these external sources rather than reproducing them in our protocol document.
Add a period.
`dist_type` for undistributed is now `n`.
Rename `data_size` to `size`.
Add constraint that `size >= 0`.
Update generated html.
Merge pull request #25 from enthought/resolve-todos

Resolve todos