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/patch.md

@@ -5,12 +5,12 @@
 
 - Apply a patch:
 
-`patch < {{patchfile}}.diff`
+`patch < {{patch_file}}.diff`
 
 - Apply a patch to current directory:
 
-`patch -p1 < {{patchfile}}.diff`
+`patch -p1 < {{patch_file}}.diff`
 
 - Apply the reverse of a patch:
 
-`patch -R < {{patchfile}}.diff`
+`patch -R < {{patch_file}}.diff`