This is not fully correct re: error handling, because we should check that
that types are used consistently (only str's or only bytes), but magically
makes lot of functions support bytes.

Should support everything supported by strings.

Addresses #567.

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.

Specifically, nlr.h does.

Share code with .strip(). TODO: optimize .rstrip().

When querying an object that supports the buffer protocol, that object
must now return a typecode (as per binary.[ch]).  This does not have to
be honoured by the caller, but can be useful for determining element
size.

Also make consistent use of MP_OBJ_NOT_SUPPORTED and MP_OBJ_NULL.
This helps a lot in debugging and understanding of function API.

mp_obj_t->subscr now does load/store/delete.

Disabled by default.  Enabled in unix port.

Similar to tuples, lists, dicts. Statically allocated strings don't have hash
computed.

This feature was proposed with initial hashing RFC, and is prerequisite for
seamless static str object definition.

These largely duplicate str() & bytes() constructors' functionality,
but can be used to achieve Python2 compatibility.

It has (again) a fast path for ints, and a simplified "slow" path for
everything else.

Also simplify the way str indexing is done (now matches tuple and list).

mp_obj_is_integer should be used to check if an object is of integral
type.  It returns true for bool, small int and long int.

stmhal relies on pfenv_* to implement its printf.  Thus, it needs a
pfenv_print_int which prints a proper 32-bit integer.  With latest
change to pfenv, this function became one that took mp_obj_t, and
extracted the integer value from that object.

To fix temporarily, pfenv_print_int has been renamed to
pfenv_print_mp_int (to indicate it takes a mp_obj_t for the int), and
pfenv_print_int has been added (which takes a normal C int).  Currently,
pfenv_print_int proxies to pfenv_print_mp_int, but this means it looses
the MSB.  Need to find a way to fix this, but the only way I can think
of will duplicate lots of code.