py: Update comment in str.replace().
py: Implement str.[r]index() and add tests for them.
py: Finish implementation of all del opcodes.

At this point, all opcodes are now implemented!

Some del opcodes have been combined with store opcodes, with the value
to store being MP_OBJ_NULL.
Merge branch 'master' of github.com:micropython/micropython
py: Remove DELETE_SUBSCR opcode, combine with STORE_SUBSCR.

This makes the runtime and object APIs more consistent.  mp_store_subscr
functionality now moved into objects (ie list and dict store_item).
py: Remove obsolete mp_delete_subscr declaration.
py: Reinstate old pfenv_print_int function for stmhal's printf.
stmhal: Make USRSW re-register the EXTI callback each time it's set.
tests: Oops: fix del-attr.
py: Add mp_get_buffer(), mp_get_buffer_raise() convenience functions to API.
objint: Implement int.from_bytes() class method and .to_bytes() method.

These two are apprerently the most concise and efficient way to convert
int to/from bytes in Python. The alternatives are struct and array modules,
but methods using them are more verbose in Python code and less efficient
in memory/cycles.
py: Add comment mpz function, and free memory used for string printing.
Merge branch 'master' of github.com:micropython/micropython
py: Make it so that printing a small int does not allocate heap memory.

With the implementation of proper string formatting, code to print a
small int was delegated to mpz_as_str_inpl (after first converting the
small int to an mpz using stack memory).  But mpz_as_str_inpl allocates
heap memory to do the conversion, so small ints needed heap memory just
to be printed.

This fix has a separate function to print small ints, which does not
allocate heap, and allocates less stack.

String formatting, printf and pfenv are now large beasts, with some
semi-duplicated code.
README: Python is required during build process unconditionally.

Fixes #449.
Fix make-pins.py to support having multiple names for a pin.

SW and X17 now both map to PB3
Merge pull request #454 from dhylands/make-pins-multiple-named-pins

Fix make-pins.py to support having multiple names for a pin.
stmhal: Add functionality to Servo object.

Can now calibrate, set pulse width, angle and speed.
stmhal: Improve help() function.
stmhal: Add windows cdc .inf driver to flash filesystem.