console: a bit better command/group handling from the prompt.
common: handle realloc to 0 size gracefully as free in debug mode.
lua-bindings: initial support for tracking Lua memory allocations.
common: added wakeup (sort of passive deferred) callback support.

Added support for wakeup callbacks to the murphy mainloop. A wakeup
callback is not quite unlike a deferred one. The crucial difference
is that wakeup callbacks do not prevent the mainloop from blocking
on (e)poll. wakeup callbacks are not executed if the mainloop is
dispatching because of active deferred callbacks (approximated by
checking if poll_timeout is 0). Using wakeup callbacks one can piggy-
back some processing on wakeups that were trigered by I/O (or signal)
events or expiring timers.
common: improved diagnostics and configurability for the debug allocator.

When running with mm debugging enabled, requesting diagnostics will
first group allocated blocks by callstack fingerprint, sort the groups
by total memory consumption and then dump the blocks. One improvement
remaining is to write a libbfd-based helper to do a better job of mapping
return addresses to function names than the stock backtrace_symbols(3) of
execinfo.

Also there is now a set of functions available to extract the value of
a given key from the configuration environment variable. This can be used
by other subsystems, for instance to decide if they need to override
default allocators of other components/libraries.
lua-bindings: use an extra boolean to control lua memory tracking.
murphy-console: support giving commands on the command line.