Add USB serial support

This changeset makes the FlySight a composite USB device, supporting
both the existing mass storage interface as well as a CDC (USB serial)
interface. This directly exposes the u-blox module to the host, which
by default yields a normal GPS stream of NMEA sentences, but being
bi-directional allows the host to reconfigure the module in whatever
manner is desired.
Update InterfaceNumbers to match enumeration

@crwper pointed this out by email. It worked on Mac OS X with the
zero interface numbers; don't ask me how.
Merge pull request #11 from willglynn/gps_via_usb_serial

Add USB serial support
Added Windows driver for virtual serial
Moved drivers to a separate folder
Actually moving the drivers this time
Merge pull request #28 from crwper/add_windows_driver

Added Windows driver for virtual serial
Moved audio folder
Merge pull request #29 from crwper/move_audio_folder

Moved audio folder
Move FlySight/ to src/ and build from the root
Added submodule init to readme
Merge pull request #31 from crwper/update_readme

Added submodule init to readme
Merge pull request #30 from willglynn/move_flysight_to_src

Move FlySight/ to src/ and build from the root
Add support for time zone offsets

FlySight normally names files and sets modification times using UTC. This
changeset adds a TZ_Offset configuration value, allowing the user to work
in local time.

The logged data retains the same format, e.g. "2013-09-04T02:02:39.50Z",
regardless of TZ_Offset, but this way a day's worth of skydives will be
stored in the same directory and with filesystem timestamps suitable for
correlating with video files or other captured data.