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/pass.md

@@ -25,4 +25,4 @@
 
 - Run any git command against the underlying store repository:
 
-`pass git {{git-arguments}}`
+`pass git {{git_arguments}}`