Moving commands section to Linux usage

Moved the commands list from terminal.md to /linux/usage/commands.md.
Also fleshed out cp and mv with more usage examples.
Resolve merge conflict
Tidy up
Merge branch 'master' of github.com:raspberrypi/documentation
More config-txt.md tweaks

Fix bad merge
Use level-4 header exclusively for config parameters
Other small changes
Change codecs header
Add empty installing Codecs page
typo
typo
Merge pull request #2 from raspberrypi/master

Syncing with origin
Additional commands and scripting usage page

Further adding descriptions of commands to commands.md. Section on
scripting from terminal.md is now it’s own separate page under
linux/usage/scripting.md.
Removed repeated sections

Composite was repeated
VGA was repeated
Merge pull request #40 from gbaman/patch-1

Remove repeated sections
Merge pull request #39 from dan-c-underwood/master

Additional commands and scripting usage page
Added link to new scripting page
Filled out networking section of commands.md

(Added details for touch, head and tail as well)
Update sonic-pi.md

Moved the call to the function frère to the section on functions as it seems to belong more naturally there than under synths
Merge pull request #43 from chrisreynolds/patch-1

Update sonic-pi.md
Merge pull request #42 from dan-c-underwood/master

Filled out networking section of commands.md
The lo interface (loopback) has no digit appended