BibField: backported improvements from pu

* Major update of BibField module with some speed improvements and
  enhancements from pu branch.

* New functional test to verify that the speed of recjson is below two
  times of that of recstruct.  (closes #1687)

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
Tested-by: Tibor Simko <tibor.simko@cern.ch>