libusbg: rename gadget_*() -> usbg_*(), libusbg, and usbg.h

Rename library to libusbg. Moves the API include to usbg.h and
accordingly changes all API prefixes to usbg_*().

Signed-off-by: Matt Porter <mporter@linaro.org>
libusbg: update preferred email address

Update email address for myself throughout the code.

Signed-off-by: Matt Porter <mporter@linaro.org>
libusbg: use /sys/kernel/config mount point in examples

Update documentation and example source code to reflect use of the
standard /sys/kernel/config mount point for configfs.

Signed-off-by: Matt Porter <mporter@linaro.org>
libusbg: tag v0.1.0 release

Update changelog and tag the v0.1.0 release.

Signed-off-by: Matt Porter <mporter@linaro.org>