MICROPY_USE_READLINE: Selects link lib, so should be defined in mpconfigport.mk

This change allows to build unix version without libreadline installed.
nlr.h: Do proper arch selection, using the same tests as nlr*.S .
nlrthumb.S: Comment out ".cpu cortex-m4", it causes problems on Cortex-A.
Add basic collections.namedtuple implementation.
Add mp_obj_is_subclass_fast() - intended for fast argument checking.

I.e. as replacement of MP_OBJ_IS_TYPE(), which takes into account subclassing.
namedtuple: Inherit unary/binary ops from tuple base class.