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/osx/du.md

@@ -4,11 +4,11 @@
 
 - Get a sum of the total size of a file/folder in human readable units:
 
-`du -sh {{file/directory}}`
+`du -sh {{file_or_directory}}`
 
 - List file sizes of a directory and any subdirectories in KB:
 
-`du -k {{file/directory}}`
+`du -k {{file_or_directory}}`
 
 - Get recursively, individual file/folder sizes in human readable form:
 

pages/osx/top.md

@@ -16,7 +16,7 @@
 
 - Start top displaying only processes owned by given user:
 
-`top -user {{user-name}}`
+`top -user {{user_name}}`
 
 - Get help about interactive commands: