Replace wc.sh with a CakeML program

developers/wc.sh is a shell script (that is probably out of date) for counting the number of lines in the CakeML repository. This issue is to replace this script with a CakeML program (we already have a wordcount program under examples) that does the same job. In particular, to figure out how to build and call the verified CakeML wordcount program, extended with arguments/functionality as required, and record this as something like a Holmake target.