Programming Language Names

"Arc"
"Clojure"
"Emacs Lisp"
"HTML"
"Haskell"
"JavaScript"
"LaTeX"
"Lisp"
"Perl"
"Python"
"Ruby"
"Ruby"
"Scheme"

Two section title changes (in a separate commit), both LaTeX, both in dsl.rmd 
A check shows that there don't seem to be any links to them.


Also fix one instance of using the spelling 'focuses' instead of 'focusses' (introduced by me in an earlier commit).