Towards addressing issue #424.

Had a small increase to ROM usage (order 60 bytes).

Implement del

This does not affect code size or performance when debugging turned off.

To address issue #420.

Change pfenv_print_int to take machine_uint_t rather than unsinged in

Allow floating point arguments with %d,i,u,o,x,X formats

py: Support 3-arg getattr() builtin (with default value).

With this change, the following works:

>>> print('%#x' % 0x1234567890abcdef)
0x1234567890abcdef

Hash table can now be completely full (ie now NULL entry) before a
resize is triggered.  Use sentinel value to indicate delete entry in the
table.

map: When removing a key, don't NULL the entry, but mark as deleted.

Quite natural to have d[int] = handle_int .

That's how CPython has it, in particular, "import __main__" should work.

When searching next time, such entry should be just skipped, not terminate
the search. It's known that marking techique is not efficient at the presense
of many removes, but namespace usage should not require many deletes, and
as for user dictionaries - well, open addressing map table with linear
rehashing and load factor of ~1 is not particularly efficient at all ;-).
TODO: May consider "shift other entries in cluster" approach as an
alternative.

Which are ESC O H, ESC O F.

Add the git version and build-date to the banner

Otherwise we have mixup between system and GC alloc.

Pointers are 2x bigger on 64 bit machines, so we should allocate twice
the memory to have a comparable heap size.