Update and cleanup licensing information

 * Removed FSF Address and replaced by link
 * Added missing license headers. The
   tomboylicense header is copied from
   the original tomboy repository at
   https://git.gnome.org/browse/tomboy
 * The configsys.{c,h} license headers were
   forgotton when the files were added.
Use strcasecmp instead of comparing characters
Compile with clang
Fix autohide bug

 * Fixes #87