unix: file: Implement .flush() method.

This method apparently should be part of stream interface.
stream: Factor out mp_stream_write() method to write a memstring to stream.
unix: file: No fsync() on Windows.
Fix teensy to build on latest tree.

Put #include of mpconfig.h before misc.h
Replace uses of ARRAY_SIZE with MP_ARRAY_SIZE
Add core files and use same toolchain as stmhal
Merge pull request #754 from dhylands/fix-teensy

Fix teensy to build on latest tree.
Merge pull request #755 from dhylands/teensy-core

Add teensy core files and use same toolchain as stmhal
py, inline asm: Change "and" op name to "and_" to avoid keyword clash.

Addresses issue #753.
formatfloat.c: Typo fix in comment.
py: Remove unnecessary argument in bytearray print.