* Also rename corresponding C sources.

* This is only one step mandated by the brain-dead behaviour of the
  NAG and PGI compilers respectively.

* lowbound is now first
* ub is now named last

This change is for two reasons:

# lowbound is a bit on the long side
# because extents of negative size are now supported, lowbound doesn't
  always represent the actual low bound

 It now uses array notation for higher dimensions.

  Fixes #19