TCTL k2 & tau updates

[sabaronett]

See https://github.com/dtamayo/reboundx/issues/64:

• tctl_tau values in C/Python examples updated to reflect correction to implementation paper manuscript (mistake caught by GDOP, Brazil).
• k1 changed to k2 to match Baronett et al. (2021)

[dtamayo]

Great! I still got confused about the k2 and had to look at the paper again. Thanks for clearing that up!

[sabaronett]

@dtamayo, have you updated the PyPI package with this change? I get the following with the latest pip install:

Traceback (most recent call last):
  File "/home/stanley/github/sabaronett/REBOUNDxPaper/fig6/gas_giants_tides.py", line 90, in <module>
    ps[0].params["tctl_k2"] = 0.038 # ~ lambda_2, Schroder & Smith (2008)
  File "/home/stanley/miniconda3/envs/rebx-3.4.0/lib/python3.9/site-packages/reboundx/params.py", line 54, in __setitem__
    raise AttributeError("REBOUNDx Error: Parameter '{0}' not found in REBOUNDx. Need to register it first.".format(key))
AttributeError: REBOUNDx Error: Parameter 'tctl_k2' not found in REBOUNDx. Need to register it first.

pip install -e . from a up-to-date cloned repo fixes it, but we may want to update PyPI sooner than later since documentation currently lists "tctl_k2".

[dtamayo]

I just pushed a new version including this commit to PyPI (3.4.1)