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/license.md

@@ -8,7 +8,7 @@
 
 - Create a license with custom filename:
 
-`license -o {{filename.txt}} {{license_name}}`
+`license -o {{filename}} {{license_name}}`
 
 - List all locally available licenses: