* Remove `dome-key-map/target/debug` from Release library search paths.
  This was causing the Release build to link against the debug version
  of dome-key-map, resulting in a 25 Mb binary.
* Strip debug symbols
* Turn on link-time optimisation

This takes the Release binary down to 1.5 Mb.

Added an `archive` target to the Makefile. This does additional
optimisations (maybe stripping symbols?), and gives us a final binary
size of 1.1 Mb. Much better.

We don't need these functions any more now that key simulation is
handled by the Rust library. The files can be safely removed.

Set 'DerivedData' path in `xcodebuild` to give us a local build
directory.

Doing this because when the 'Debug', or 'Release' directories in
'Build/Products/' don't exist, Make doesn't build our recipes. Make
seems to prefer local files, and I don't imagine the wildcard in the
path does us any favours.

When I changed the DerivedData path, I ended up with this error:

    In file included from DomeKey/DomeKey/HeadphoneKey.m:9:
    DomeKey/DomeKey/HeadphoneKey.h:10:9: fatal error:
          'DDHidLib/DDHidAppleMikey.h' file not found
    #import <DDHidLib/DDHidAppleMikey.h>
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Couldn't figure out what the problem was, and what changed there when I
changed the DerivedData directory. So I just fixed it in the only way I
could think of: adding the DDHidLib 'lib' directory to
`HEADER_SEARCH_PATHS` and updating the `#import` to point to the new
location.

We also create a release target in this commit, which gives us a release
build of the program.

A new function to print to stderr prefixed with a timestamp. The idea is
to make the printed line's format match the Rust logger's.

The Rust logger prints timestamps like this:

    2018-11-04T03:16:31.938+01:00

`teprintf` does:

    2018-11-04T15:02:21+0100

Unfortunately, I wasn't able to reproduce it exactly. It's missing the
milliseconds because I didn't want to deal with using `gettimeofday`,
and the time zone format isn't right because I didn't know how to format
it easily with a colon.

Resources:
Getting the time in C:
https://stackoverflow.com/questions/9596945/how-to-get-appropriate-timestamp-in-c-for-logs#9596994

Variadic functions in C:
https://stackoverflow.com/questions/205529/passing-variable-number-of-arguments-around

Getting milliseconds in C:
https://stackoverflow.com/questions/10192903/time-in-milliseconds#10192994
https://stackoverflow.com/questions/3673226/how-to-print-time-in-format-2009-08-10-181754-811
https://stackoverflow.com/questions/361363/how-to-measure-time-in-milliseconds-using-ansi-c

Concatenating strings in C:
https://stackoverflow.com/questions/308695/how-do-i-concatenate-const-literal-strings-in-c#308712
https://stackoverflow.com/questions/8465006/how-do-i-concatenate-two-strings-in-c

This will be used to play the mode activated & deactivated sounds via
`NSSound` (hopefully).

We're no longer using this code. Keyboard simulation has been moved
since a long while ago to the Rust library using the 'autopilot'
library.

This was a test to see if we could get Bluetooth headphone events using
media key events. I wasn't successful. Get rid of the code now that it
isn't being used.

For interacting with XDG directories.

This class will encapsulate all license and trial handling.

Turns out the build had failed previously because the linked Rust
library expects 10.7. Change the deployment target to match and now it
works.