Continuation of refactoring applied previously to objlist.

This is intended to improve coverage of the test suite.

It allowed such things as (a, b) += c.

Saves around 30 bytes code on Thumb2 archs.

This allows to properly initialize the system led and add it
to the sleep module so that it can be restored when resuming
from suspended mode.

Unfortunately, these timeouts are the only realiable way (for now), to
be able to detect broken connections due to half-open sockets. Such a
thing occurs when getting out of the WiFi coverage area or when
disconnecting from the AP (sometimes the client doesn't send the
disconnect packet).

mp_obj_t internal representation doesn't have to be a pointer to object,
it can be anything.

There's also a support for back-conversion in the form of MP_OBJ_UNCAST.
This is kind of optimization/status quo preserver to minimize patching the
existing code and avoid doing potentially expensive MP_OBJ_CAST over and
over. But then one may imagine implementations where MP_OBJ_UNCAST is very
expensive. But such implementations are unlikely interesting in practice.

This change is required to unbreak some CPython stdlib modules (as included
into micropython-lib).

The 2 removed from coverage build are: -Wredundant-decls and
-Wstrict-prototypes.

To have proper low power mode, need to configure all unused pins in
input mode, so need to have them available.

This can get PYBv1.0 stop current down to around 290uA.

Despite initial guess, this code factoring does not hamper performance.
In fact it seems to improve speed by a little: running pystone(1.2) on
pyboard (which gives a very stable result) this patch takes pystones
from 1729.51 up to 1742.16.  Also, pystones on x64 increase by around
the same proportion (but it's much noisier).

Taking a look at the generated machine code, stack usage with this patch
is unchanged, and call is tail-optimised with all arguments in
registers.  Code size decreases by about 50 bytes on Thumb2 archs.

Only MASTER mode is supported. Transfer width is configurable to
8, 16 or 32 bits.

Without that, "import http.client" failed due to max recursion.

This also cleans up spurious interrupts which happen at timer
initilaization time.

Disabled by default.  Enabled on unix and stmhal ports.

"Base" should rather refer to "base type"."Base object for attribute
lookup" should rather be just "object".

Also, a case of common subexpression elimination.