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/prt-get.md

@@ -4,19 +4,19 @@
 
 - Install a package:
 
-`prt-get install {{package-name}}`
+`prt-get install {{package_name}}`
 
 - Install a package with dependency handling:
 
-`prt-get depinst {{package-name}}`
+`prt-get depinst {{package_name}}`
 
 - Update a package manually:
 
-`prt-get upgrade {{package-name}}`
+`prt-get upgrade {{package_name}}`
 
 - Remove a package:
 
-`prt-get remove {{package-name}}`
+`prt-get remove {{package_name}}`
 
 - Upgrade the system from the local ports tree:
 
@@ -24,7 +24,7 @@
 
 - Search the ports tree:
 
-`prt-get search {{package-name}}`
+`prt-get search {{package_name}}`
 
 - Search for a file in a package: