Recognise *.dyalog as APL sources

The recommended extension for [Dyalog](http://dyalog.com/) "script files" (i.e. functions, namespaces, classes, etc that aren't stored in a "workspace") is `.dyalog`.  Dyalog's dialect has its own additions to the language but at its core it's compatible with what is traditionally known as APL, so I think it should be highlighted as such.