These are micropython.mem_total(), .mem_current(), .mem_peak(). These are 3
individual functions with simple scalar return value to make sure that
calls to these functions themselves have minimal (hopefully zero) impact on
memory allocation.
A big change. Micro Python objects are allocated as individual structs
with the first element being a pointer to the type information (which
is itself an object). This scheme follows CPython. Much more flexible,
not necessarily slower, uses same heap memory, and can allocate objects
statically.
Also change name prefix, from py_ to mp_ (mp for Micro Python).
