Now much more inline with how CPython does types.

With MICROPY_EMIT_X64 and MICROPY_EMIT_THUMB disabled, the respective
emitters and assemblers will not be included in the code.  This can
significantly reduce binary size for unix version.

So far, only start and stop integer indexes are supported. Step is
not supported, as well as objects of arbitrary types.

mpconfig.h will automatically pull mpconfigport.h.

import works for simple cases.  Still work to do on finding the right
script, and setting globals/locals correctly when running an imported
function.

termcap is not needed on Linux.  Need to work out how to automatically
configure the Makefile...

E.g.:
/usr/lib/libreadline.so.4.0: undefined reference to `tgetnum'
/usr/lib/libreadline.so.4.0: undefined reference to `tgoto'
/usr/lib/libreadline.so.4.0: undefined reference to `tgetflag'
/usr/lib/libreadline.so.4.0: undefined reference to `tputs'
/usr/lib/libreadline.so.4.0: undefined reference to `tgetent'
/usr/lib/libreadline.so.4.0: undefined reference to `tgetstr'

Tested on linux too, works.

Readline is GPL, so linking with it casts the binary GPL.

A big change.  Micro Python objects are allocated as individual structs
with the first element being a pointer to the type information (which
is itself an object).  This scheme follows CPython.  Much more flexible,
not necessarily slower, uses same heap memory, and can allocate objects
statically.

Also change name prefix, from py_ to mp_ (mp for Micro Python).