Implement a basic str.find; fixes #67

Elaborate small-int/long-int

Set features. As per #143.

Added a hacky implementation for %g

See pyb_usart_global_debug variable.

Also did some work on USB OTG, but nothing working yet.

Long int is something which doesn't fit into SMALL_INT partion of
machine_int_t. But it's also something which doesn't fit into
machine_int_t in the first place.

We likely should make mp_obj_new_int() inline, and rely on its
encapsulated check rather than inline checks everywhere explicitly.

Also, parser for big small int values is still broken.

Small graphic - Useful for WebBanners, etc...

Implement type virtual equality method support and implement comparisons for lists

Added memzip filesystem support for teensy

Add AssertionError.

Currently it would report "operation not supported" which is confusing. Overall,
this is thinko leading to undefined behavior.

You can now append a zipfile (containining uncomressed python sources)
to the micropython.hex file.

Use MEMZIP_DIR=directory when you call make, or set that in your
environment to include a different tree of source files.

Added sample /boot.py, /src/main.py, /test.py and /src/test.py files.

Added run command so that you can execute scripts from REPL (until import is implemented).

Added build directory to .gitignore

Still need to make built-ins by these names, and write tests.