Remove param from python API of ext_register

Minor cleanup.
Merge pull request #329 from dhylands/exti-cleanup

Remove param from python API of ext_register
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.
py: Implement bit-shift and not operations for mpz.

Implement not, shl and shr in mpz library.  Add function to create mpzs
on the stack, used for memory efficiency when rhs is a small int.
Factor out code to parse base-prefix of number into a dedicated function.
Merge pull request #330 from pfalcon/cortex-a

Support building "unix" port for ARM
Implement machine_sqrt using VSQRT
Merge pull request #331 from iabdalkader/master

Implement machine_sqrt using VSQRT
unix: Add GC support for ARM architecture.
Merge remote-tracking branch