utility/event: add new module

Derived from work on radio state machines, this new capability supports
ordered timestamped events with associated data, as well as simple edge
and level triggered signals.
examples/event: show execution statistics

Display number of times each MUX alarm interrupt fired and the active
main-loop duty cycle.
unittest: support 64-bit integer comparisons
timer: support reading full-precision times and correcting them

As we start to do more with NTP, having the full-precision available
only as a 32-bit low and 16-bit overflow counter is inconvenient.
Provide a way to return the 48-bit counter as a 64-bit integer.

Also provide a way to adjust that value so that a full-precision
representation of a timestamp captured in hardware as a 16-bit counter
has the correct corresponding setting for the upper 48 bits regardless
of subsequent overflow (so long as the 16-bit counter did not lap
itself).
port: expand SET_REN macros to no-ops when REN not supported

This eliminates conditional code in applications, at a cost of not
notifying the developer when REN functionality is absent.
serial: add facility to get bus/baud rate
timer: support reading counter for mux timer base
utility/event: add periodic event support

There's a common need to do things periodically; don't make every
application code its own infrastructure for doing so.  This version only
supports event tags, not event flags, as it passes the configuration
data for the periodic event in the event record.
eui64: add uint64_t access to EUI64
utility/event: refine description of periodic event fields

A casual reader might think it possible to change the interval to stop
repetition after the next event.  While theoretically this might be
useful, it's best not to mutate the values of fields read in an ISR, so
disallow it.  Implement timely processing of the event and cancel it
there, or use a non-event muxalarm callback.
utility/uptime: add routine for human-readable scaled time

For displaying a wide range of durations it's nicer to convert ticks to
something smaller and understandable.
core: include stdbool.h

We already require C99 for various anonymous struct/union types, so go
ahead and use stdbool as well.
uptime: add support for measuring application duty cycle
eui64: refine null/invalid value management

Not sure why the all-1s EUI-64 was used for NULL, as the all-0s version
makes more sense.  Codify use of the all-1s EUI-64 to denote an invalid
value as opposed to an unassigned value; this is more consistent with
the practice of zeroing a structure to create an initial state.
uptime: add utilities for identifying and adjusting special uptime values

Special identifying values for uptime might occur in a couple
situations: when using an interrupt-captured signal to transmit local
time to another node through an RF interface, an initialized value of
zero might indicate that the captured time was not written into the
packet before transmission occurred.

Analogously, an initialized value of ~0UL might indicate that sensor
samples corresponding to that time are not available.

Provide a facility to distinguish times from these identifying values,
and to adjust valid times so they do not happen to match one of these
values.
onewire: fix issues with high MCLK rates

If MCLK is configured greater than about 8MHz, the calculation of cycle
counts for reset overflow the 32-bit representation used.  Widen the
representation, and document the potential issue in the general API.
newlib: add support for nosys

This commit provides stub implementations for sbrk(2) and other system
calls that newlib expects to be provided by the environment.
console: default provide stdio infrastructure for newlib

The weak nosys defaults don't support any read/write infrastructure.
Life is simpler if printf() and putchar() just work, so unless told
otherwise use the console infrastructure to provide this.
bootstrap: add stdconsole example

This uses the newlib infrastructure for libc to do character I/O with
standard functions.
Makefile.common: support providing custom linker script

Since TI-supplied scripts don't support far ROM natively, provide a
mechanism to specify alternative scripts.