Add docstrings to `mseedpull.py` and `ooipull.py`

[`mseedpull.py`](https://github.com/orcasound/orcanode/blob/master/mseed/mseedpull.py)
[`ooipull.py`](https://github.com/orcasound/orcanode/blob/master/mseed/ooipypull.py)

- [ ] header docstrings
- [ ] doctrings to individual functions