Change the API of MArray to allow resizable arrays

Change the API of MArray to allow resizable arrays
See #704

The MArray class doesn't currently allow a mutable array to change its
size, because of the pure function

  bounds :: (HasBounds a, Ix i) => a i e -> (i,i)

This patch removes the HasBounds class, and adds

  getBounds :: (MArray a e m, Ix i) => a i e -> m (i,i)

to the MArray class, and

  bounds :: (IArray a e, Ix i) => a i e -> (i,i)

to the IArray class.

The reason that bounds had to be incorporated into the IArray class is
because I couldn't make DiffArray work without doing this.  DiffArray
acts as a layer converting an MArray into an IArray, and there was no
way (that I could find) to define an instance of HasBounds for
DiffArray.