likelihood updates for cobaya devel branch

[xzackli]

Updates for the cobaya devel branch.

[xzackli]

Tests pass on Linux. I've disabled the mflike tests since that feature is still in development.

============== test session starts ==============
platform linux -- Python 3.8.2, pytest-5.4.1, py-1.8.1, pluggy-0.13.1
rootdir: /home/zequnl/src/Likelihoods
plugins: hypothesis-5.5.4, astropy-header-0.1.2, openfiles-0.4.0, remotedata-0.3.2, arraydiff-0.2, doctestplus-0.5.0, forked-1.1.3, flaky-3.6.1
collected 8 items                                                                                                                                                        

solike/tests/test_clusters.py .                                                                                                                                    [ 12%]
solike/tests/test_gaussian.py .                                                                                                                                    [ 25%]
solike/tests/test_lensing.py ..                                                                                                                                    [ 50%]
solike/tests/test_mflike.py s                                                                                                                                      [ 62%]
solike/tests/test_multi.py s                                                                                                                                       [ 75%]
solike/tests/test_poisson.py .                                                                                                                                     [ 87%]
solike/tests/test_ps.py .                                                                                                                                          [100%]

============== warnings summary ==============
/home/zequnl/.local/lib/python3.8/site-packages/PyWCSTools/wcs.py:13
  /home/zequnl/.local/lib/python3.8/site-packages/PyWCSTools/wcs.py:13: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
    import imp

-- Docs: https://docs.pytest.org/en/latest/warnings.html
============== 6 passed, 2 skipped, 1 warning in 27.51s ==============