Add support for Application Get Telemetry

[mablem8]

• Add a description of Application Get Telemetry to DOCUMENTATION.md
• Add Application Get Telemetry to c-implementation/tab.c with an external handler
• Add a handler implementation of Application Get Telemetry to cdh.c
• Add a handler implementation of Application Get Telemetry to com.c
• Add an implementation of Application Get Telemetry to python-implementation/tab.py
• Add testing of Application Get Telemetry in python-examples/tx/tx_example.py
• Test support for Application Get Telemetry with c-examples/cdh-monolithic and python-examples/tx

[AnandAlok0807]

Commit 2e36726 fixes issue 29.

Result : tab_examples.py tab command
txcmd: application_get_telem hw_id:0x1234 msg_id:0x000c src:gnd dst:cdh
reply: common_ack hw_id:0x1234 msg_id:0x000c src:cdh dst:gnd