Addresses issue #290, and hopefully sets up things to allow generators
throwing exceptions, etc.

First arg is not alloc size, but real size, so if used as
mp_obj_new_list(3, NULL), need to store items, not append.

Thanks to @pfalcon for the tip!

Each built-in exception is now a type, with base type BaseException.
C exceptions are created by passing a pointer to the exception type to
make an instance of.  When raising an exception from the VM, an
instance is created automatically if an exception type is raised (as
opposed to an exception instance).

Exception matching (RT_BINARY_OP_EXCEPTION_MATCH) is now proper.

Handling of parse error changed to match new exceptions.

mp_const_type renamed to mp_type_type for consistency.

Ultimately all static strings should be qstr.  This entry in the type
structure is only used for printing error messages (to tell the type of
the bad argument), and printing objects that don't supply a .print method.

Issue #290. This currently fails, to draw attention to the issue.

OS X compatible -map syntax for LDFLAGS

Allow ports to define statically builtin functions.

Implement "from mod import *"

Done by introducing another factored out helper API in binary.c. This API
can be reused also by array and struct modules.

Convert unix open() to such.

unix Makefile: Split off optimization options to COPT variable.

To allow easily try different optimization and configuration options
without patching any files.

Some tools do not support local/static symbols (one example is GNU ld map file).
Exposing all functions will allow to do detailed size comparisons, etc.

Also, added bunch of statics where they were missing, and replaced few identity
functions with global mp_identity().

For some reason, STM port, while it's 32 bit, needs %lu and %ld for
printing machine_uint_t and machine_int_t.

Enable GC for Unix port

Enable link map file generation.

Bah - Removed a couple of warnings for teensy that I didn't notice before.

Note: none of these functions are used by STM port, so they're provided
to have parity with pre gc refactor status quo, and in case they will be
needed in the future by some extension writers.