py/mpprint: Add %o/%r formatting code to print str()/repr() of an mp_obj_t.
py/mpprint: Add %o/%r formatting code to print str()/repr() of an mp_obj_t.

Similar to existing "%q" to pring a qstr. The usefulness of such addition
was long discussed. In particular, it would be useful to dynamic modules,
to expose only mp_printf() to them, and not the all extra helper functions.

Change-Id: I2f7ca599111f7b7d5e65105f3c4572fd6c632895

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython