Better source unifier

- now it is called scripts/unify-sources.sh
- replaces each tab with 8 spaces
- remove trailing spaces (and tabs)
- warnings on long lines (i.e. on lines that are more than 80 characters)
- the standard file header now turns off the space-to-tab replacement in Emacs

 project (LEMON)

 enable_testing ()

 add_subdirectory (lemon)

 add_subdirectory (demo)

 add_subdirectory (test)