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/transcode.md

@@ -5,12 +5,12 @@
 
 - Create stabilisation file to be able to remove camera shakes:
 
-`transcode -J stabilize -i {{inputfile}}`
+`transcode -J stabilize -i {{input_file}}`
 
 - Remove camera shakes after creating stabilisation file, transform video using xvid:
 
-`transcode -J transform -i {{inputfile}} -y xvid -o {{outputfile}}`
+`transcode -J transform -i {{input_file}} -y xvid -o {{output_file}}`
 
 - Resize the video to 640x480 pixels and convert to MPEG4 codec using xvid:
 
-`transcode -Z 640x480 -i {{inputfile}} -y xvid -o {{outputfile}}`
+`transcode -Z 640x480 -i {{input_file}} -y xvid -o {{output_file}}`