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/ln.md

@@ -8,7 +8,7 @@
 
 - Overwrite an existing symbolic to point to a different file:
 
-`ln -sf {{path/to/new/file}} {{path/to/symlink}}`
+`ln -sf {{path/to/new_file}} {{path/to/symlink}}`
 
 - Create a hard link to a file: