np.average, find_hip, astroquery

[mzechmeister]

Some more suggestions:

1. Use np.average for the weighted means.
2. Move find_hip to utils where get_stellar_data is located. Or even consider to make it part of get_stellar_data, e.g. get_stellar_data(name='', hip_id=None).
3. Make astroquery import optional with a try. It adds more dependencies which are not necessarily needed for get_BC_vel. I have not installed it, since have created my own request tool (https://github.com/mzechmeister/serval/blob/master/src/targ.py)

[shbhuk]

Fixed 2. in 1e276b6

[shbhuk]

Fixed 3. in cde9c1a

[shbhuk]

For 1. I think I shall leave it this way, is more explicit and easier to understand if anyone looks at the source code.