Pymata-express

1. Support for DHT humidity/temperature sensors added.
2. Support for StandardFirmataWiFi added.
3. Incorporated pull request 18 to optionally allow loop to stay open on shutdown.

This release fixes issue 15

This release addresses and closes the following issues:
1. issue 12
2. issue 13
3. issue 14

NOTE: That there are breaking changes for the data provided to callback functions:

| Callback | Prior To Version 1.11| Version 1.11 And Above |
|---------------------- |--------------|------|
| analog input | [pin, current reported value, pin_mode, timestamp]| [pin_mode = 2, pin, current reported value, pin_mode, timestamp] |
| digital input |[pin, current reported value, pin_mode, timestamp]| [pin_mode = 0, pin, current reported value, pin_mode, timestamp]| |
| hc-sr04| [pin, distance] | [pin_mode=12, trigger pin number, distance, timestamp]|
| i2c | [Device address, data bytes] |[pin_mode=6, i2c device address, data bytes, timestamp]|

Other than the version number in private_constants.py, no other changes.

Only destroy tasks created by the library.