Enum: add __getitem__ so we can map back from value to string

We need to be able to map values back to strings for enums too,
so that if get a value from the device we can convert it into a nice
human readable string.

Add enums to inquiry and add an example to the inquiry test tool
to show why we want to be able to INQUIRY.DEVICE_TYPE[<value>] -> string

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Merge pull request #6 from sahlberg/inquiry-enums

Enum: add __getitem__ so we can map back from value to string