Replace hbcxx::startswith with boost::starts_with

This removes some code and corrects a bit of NIH.

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
Include a stopwatch example.

A stopwatch is the sort of program I would historically implement
using shell script (and usleep) but this version, written in C++, can
be both more robust whilst having fewer wakeups (thus taxing the battery
rather less).

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
Fix return code and signal propagation from the child process.

Oops! I meant to fix the return code propagation before the first
public announcement. As it happens I don't feel nearly as much shame
about taking my time to get the signal handling exactly right!

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
Add to the TODO list.

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>