Applying the snake_case convention throughout the repo (#967)

* Applying the snake_case convention throughout the repo

- Also removing the file extension where not needed
- Adding {{ }} on a few old pages

* Addressing concerns

- Added {{ }} where they were missed out
- Removed spaces inside {{ }}
- Reverting "file" to "filename" to make it clearer

* Fixing the comments on nc page

pages/common/autossh.md

@@ -25,4 +25,4 @@
 
 - Run autossh in the background with debug output logged to a file and ssh verbose output logged to a second file:
 
-`AUTOSSH_DEBUG=1 AUTOSSH_LOGFILE={{log_file}} autossh -f -M {{monitor_port}} -v -E {{ssh_logfile}} {{ssh_command}}`
+`AUTOSSH_DEBUG=1 AUTOSSH_LOGFILE={{log_file}} autossh -f -M {{monitor_port}} -v -E {{ssh_log_file}} {{ssh_command}}`