Custom microclustering and beta-yields generator

[PavelKavrigin]

• Added the first version of beta-yields quanta generator based on BiPo single beta measurement;
• Added custom track-topology-based microclustering: (a) 'betadecay' which clusters separately the gamma and the beta of a beta-decay; (b) 'brem' which separates Bremsstrahlung gamma clusters in addition to separating beta- and gamma-products of a decay.

[ramirezdiego]

Hi Pavel, this looks very good, thanks a lot. Please address the comment below plus:

• add the new options in the README file

Otherwise we're ready to go :)