Changed 'enrol' (BE) to 'enroll' (AE)

bob/learn/em/cpp/ISVTrainer.cpp

bob/learn/em/cpp/JFATrainer.cpp

bob/learn/em/cpp/PLDAMachine.cpp

bob/learn/em/cpp/PLDATrainer.cpp

bob/learn/em/cpp/ZTNorm.cpp

bob/learn/em/include/bob.learn.em/ISVMachine.h

bob/learn/em/include/bob.learn.em/ISVTrainer.h

bob/learn/em/include/bob.learn.em/JFAMachine.h

bob/learn/em/include/bob.learn.em/JFATrainer.h

bob/learn/em/include/bob.learn.em/PLDATrainer.h

bob/learn/em/isv_trainer.cpp

bob/learn/em/jfa_trainer.cpp

bob/learn/em/plda_trainer.cpp

bob/learn/em/test/test_jfa_trainer.py

bob/learn/em/test/test_plda_trainer.py

doc/guide.rst