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/gzip.md

@@ -8,16 +8,16 @@
 
 - Decompress a file, replacing it with the original uncompressed version:
 
-`gzip -d {{file.ext.gz}}`
+`gzip -d {{file.ext}}.gz`
 
 - Compress a file specifying the output filename:
 
-`gzip -c {{file.ext}} > compressed-file.ext.gz`
+`gzip -c {{file.ext}} > {{compressed_file.ext}}.gz`
 
 - Uncompress a gzipped file specifying the output filename:
 
-`gzip -c -d {{file.ext.gz}} > uncompressed-file.ext`
+`gzip -c -d {{file.ext}}.gz > {{uncompressed_file.ext}}`
 
 - Specify the compression level. 1=Fastest (Worst), 9=Slowest (Best), Default level is 6:
 
-`gzip -9 -c {{file.ext}} > compressed-file.ext.gz`
+`gzip -9 -c {{file.ext}} > {{compressed_file.ext}}.gz`