`set_n_posterior_samples` and `set_n_somethings` in general

[MichaelClerx]

Hey all,

Recent change to nested sampling changed a method set_posterior_samples to set_n_posterior_samples. This is more clear, but wondering if it's consistent.

For example, (1) there's also a set_iterations in the same class that sets the number of iterations, and searching for set_n_ methods in general I only find them in the updated nested code.

Thoughts @ben18785 @martinjrobins @fcooper8472 @chonlei ?