Add dylanlid-mode for highlighting of lid files

Also let's you click on files with mouse1 to open them.
Make xrefs clickable.
Merge pull request #20 from dylan-lang/clickable-xrefs

Make xrefs clickable.
whitespace-fixes
check for existance of program before executing, and provide a message if the program does not exist
Merge pull request #21 from dylan-lang/fixes

Fixes
Merge pull request #22 from erikcharlebois/master

Add dylanlid-mode for highlighting of lid files
Load dylanlid-mode.