Switch element ordering in window tuples to row,column.

Internally, we often say "j, i".

Also, have added a (j, i) index tuple to the value returned by
block_windows, making it a bit like Python's enumerate() func.

See #13.
Add a doc about windowed reads and writes.
Oops, indexing confusion corrected.
Change indexing in the prose, too.
Add ndarray reading benchmarks.
Switch to range/slice-like windows.

Many more tests added and documentation underway.

See #13.
Add another test of window_index function.

Again, see #13.
Simple reading and writing examples.

See #13.
Decimation example.

See #13.
Advanced windows and blocks documentation added.

Closes #13.