Measure speed of each tool for celestial conversions

* Currently astropy is 100 to 10,000 times slower than the other tools (see attached `speed.txt` file)
https://github.com/astropy/coordinates-benchmark/blob/master/docs/Tools.rst
* pyast is fastest (congratulations @dsberry)

astropy is slow because instantiating the coordinate classes is slow, not because transformations as slow:
```
In [24]: from astropy import coordinates

In [26]: %timeit coordinates.FK4Coordinates(0, 0, unit='deg')
100 loops, best of 3: 5.68 ms per loop

In [27]: c =  coordinates.FK4Coordinates(0, 0, unit='deg')

In [29]: %timeit c.transform_to(coordinates.FK5Coordinates)
1000 loops, best of 3: 238 us per loop
```

@eteq Why is creating an astropy coordinate object so slow? Can this be sped up easily?
Instantiating a `Position` object in `astrolib.coords` is 1000 times faster:
```
In [36]: import coords

In [37]: %timeit coords.Position((0,0))
100000 loops, best of 3: 4.89 us per loop
```