Add a variety of IBA::colorconvert that takes the color space names
Add ImageBufAlgo::ociolook()
ImageBufAlgo refactor -- eschew in-place operations

The vast majority of IBA functions take a dst and one or more source
images, and operate by copying data from the source(s) to the destination
while doing some computations on the values.  A small minority instead
operated "in-place".  For the sake of uniformity, I have decided to
deprecate the in-place operations in lieu of always taking a destination
argument (in many functions, however, it's perfectly legal for dst to
refer to the same image as src, and the docs point this out).

To serve this end, this patch does the following:

* Deprecate the in-place varieties of IBA add, sub, mul, rangecompress,
  rangeexpand, unpremult, premult, clamp, fixNonFinite.  Add new
  "copying" varieties (which can be made to operate in-place merely by
  specifying the same image for src and dst).

* Add sub() varieties that take float or float* operand (did not exist
  before).

* Remove other IBA functions that were deprecated in 1.2 (and adjust a
  few places where we still used the deprecated versions).

* Add testsuite tests for oiiotool --rangecompress and --rangeexpand.
ImageBufAlgo header & docs -- fix typos, formatting, clarify docs
Python bindings for ImageBufAlgo

The vast majority of ImageBufAlgo functions are hereby exposed to Python.

A small number of functions have temporarily been omitted.  These are
all rarely used, and had call signatures where I was unsure of the
correct Pythonic way to organize them.  We'll come back to this later,
but in the mean time, we have now working versions of almost everything
else in ImageBufAlgo that you can use from Python.
Documentation for ImageBufAlgo Python bindings