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.
stmhal: Add file.flush and os.stat.
py: Add stream reading of n unicode chars; unicode support by default.

With unicode enabled, this patch allows reading a fixed number of
characters from text-mode streams; eg file.read(5) will read 5 unicode
chars, which can made of more than 5 bytes.

For an ASCII stream (ie no chars > 127) it only needs to do 1 read.  If
there are lots of non-ASCII chars in a stream, then it needs multiple
reads of the underlying object.

Adds a new test for this case.  Enables unicode support by default on
unix and stmhal ports.