version 1.2.1

In this release, we have implemented new features in pipeline modules:

1. users can chose which likelihood solver/sampler to use:

• pipeline.solver = "minuit" : use iminuit as solver
• pipeline.solver = "emcee" : use emcee as Bayesian sampler
• pipeline.solver = "dynesty" : user dynesty as Bayesian sampler

2. we upgraded the pstimator.target input form:
   previously we use a string as the input form, now we change it to a tuple of strings, e.g.,

• ("EE",) : estimate EE mode only
• ("EE", "BB") : estimate EE and BB modes

(fixed the indentation issue of v1.2.0)