Feature/handles

[hbldh]

Merges #167 by means of new branch.

Changed some details of #167 to handle characteristics a bit differently.
read_gatt_char, write_gatt_char, start_notify and stop_notify now accepts

• BleakGATTCharacteristics objects
• integer handler for the characteristic to use
• string uuid
• uuid.UUID objects

The efficiency of using the different solutions are in that descending order as well. It is now less effective than before to use string representations of the UUIDs of a characteristic, this is an effect of keeping track of characteristics is done by integer handles instead of string uuids. This will hopefully fix #139 and #159.

[geeksville]

yay!