Add support for Application Telemetry

[mablem8]

The Application Telemetry command should be similar to a Common Data command, e.g., remaining bytes must be greater than or equal to 0x07. However, the Application Telemetry command is also similar to the Bootloader Ack command in that, because the command is used as a reply, sending this command generates a common nack reply.

• Add a description of Application Telemetry to DOCUMENTATION.md
• Add Application Telemetry to c-implementation/tab.c with an external handler (edit: no handler needed)
• Add a handler implementation of Application Telemetry to cdh.c (edit: no handler needed)
• Add a handler implementation of Application Telemetry to com.c (edit: no handler needed)
• Add an implementation of Application Telemetry to python-implementation/tab.py
• Add testing of Application Telemetry in python-examples/tx/tx_example.py
• Test support for Application Telemetry with c-examples/cdh-monolithic and python-examples/tx

[AbhishekCMU]

Commit beaee31 fixes issue-28.

1. Changes in file tab.c at line 266
2. Changes in file tab.h at line 36
3. Changes in file tx_example.py at line 281
4. Changes in file tab.py at line 33, 234, 329, 388
5. Documentation update in DOCUMENTATION.md for addition of application telemetry.

Output : from running tab command tx_examples.py
txcmd: application_telem hw_id:0x1234 msg_id:0x000c src:gnd dst:cdh
reply: common_nack hw_id:0x1234 msg_id:0x000c src:cdh dst:gnd