Allow customize proposal choice, and varying ntrials in parameter splitting.
modifications proposed:
- created a chain and sampler argument to customize the function for choosing proposal. It defaults to the usual one (picking up one proposal randomly according to weights)
- modified the PS Chain so that the number of fast trials can be modified according to the proposal
- added an history method to the PS Chain so that running with the
profiling
option does not fail
@maudelejeune , can you please have a quick look before merging.