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/linux/pkginfo.md

@@ -8,7 +8,7 @@
 
 - List files owned by a package:
 
-`pkginfo -l {{package-name}}`
+`pkginfo -l {{package_name}}`
 
 - List the owner(s) of files matching a pattern: