New tool: Miriade

Miriade is the ephemeris server of the IMCCE: http://vo.imcce.fr/webservices/miriade/
For now, only the `rts` (rise, transit, set) method is implemented.

    >>> from astroquery import miriade
    >>> m = miriade.Miriade()
    >>> m.query_rise_transit_set('2014-07-15', 'sun', 'paranal')
    name    date     riseH    riseA  transitH transitE   setH     setA   dawnA    dawnN    dawnC   twilightC twilightN twilightA
                     h:m:s     deg    h:m:s     deg     h:m:s     deg    h:m:s    h:m:s    h:m:s     h:m:s     h:m:s     h:m:s  
    ---- ---------- -------- ------- -------- -------- -------- ------- -------- -------- -------- --------- --------- ---------
     Sun 2014-07-15 11:25:58 -113.40 16:47:36    44.10 22:09:23  113.40 10:04:49 10:32:25 11:00:24  22:34:58  23:02:57  23:30:33

The conversion from the observatory names to longitude and latitude is done using the list from the minor planet center: http://www.minorplanetcenter.net/iau/lists/ObsCodes.html

As always (from me), the documentation and the tests are missing. Do not merge yet...
Make the URL a configuration item?