example failures

Hi @GregAshton, two issues I found with running examples on current master, the first in transient_search_using_MCMC.py and apparently related to the ptemcee move and hence I'm not sure how to debug it:

12:12 INFO : Running final burn and prod with 200 steps 0%| | 0/200 [00:00<?, ?it/s]Traceback (most recent call last): File "examples/other_examples/transient_search_using_MCMC.py", line 47, in <module> mcmc.run() File "/home/dkeitel/git/PyFstat/pyfstat/mcmc_based_searches.py", line 522, in run sampler = self._run_sampler(sampler, p0, nburn=nburn, nprod=nprod) File "/home/dkeitel/git/PyFstat/pyfstat/mcmc_based_searches.py", line 388, in _run_sampler total=nburn+nprod): File "/home/dkeitel/.local/lib/python2.7/site-packages/tqdm/_tqdm.py", line 862, in __iter__ for obj in iterable: File "/home/dkeitel/.local/lib/python2.7/site-packages/ptemcee/sampler.py", line 355, in sample raise ValueError('Attempting to start with samples outside posterior support.') ValueError: Attempting to start with samples outside posterior support.

Probably more trivial to fix is fully_coherent_search_using_MCMC.py which runs mostly through but gives at the end:

Traceback (most recent call last): File "fully_coherent_search_using_MCMC.py", line 60, in <module> mcmc.run(subtractions=[F0, F1]) File "/home/dkeitel/git/PyFstat/pyfstat/mcmc_based_searches.py", line 524, in run fig, axes = self._plot_walkers(sampler, nprod=nprod, **kwargs) TypeError: _plot_walkers() got an unexpected keyword argument 'subtractions'

Is it safe to just remove that argument, or is there a replacement?