Create an MCMC instance

def createMCMC(config,srcfile,section='source',samples=None):
    """ Create an MCMC instance """

    source = ugali.analysis.source.Source()
    source.load(srcfile,section=section)
    loglike = ugali.analysis.loglike.createLoglike(config,source)

    mcmc = MCMC(config,loglike)
    if samples is not None:
        mcmc.load_samples(samples)

    return mcmc