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/emerge.md

@@ -16,11 +16,11 @@
 
 - Install a new package, with confirmation:
 
-`emerge -av {{package-name}}`
+`emerge -av {{package_name}}`
 
 - Remove a package, with confirmation:
 
-`emerge -Cav {{package-name}}`
+`emerge -Cav {{package_name}}`
 
 - Remove orphaned packages (that were installed only as dependencies):