Fix byte compilation warnings

Alias `user-error` while compiling, too, to avoid undefined function
errors when byte compiling under Emacs 24.2.
[Fix #57] Guard the definition of fringe bitmaps
Put first checker error on top

Add overlays from last to first error so that for each error region the
first error emitted by the checker is stacked on top.
Fix author and copyright information
Do not mess up error match data

s functions may change the match data, thus we need to restore this
match data in order to safely continue error parsing afterwards.

Why oh why did they make the match data global?!  Now I just hate you,
dear Emacs…
Fix arguments of Emacs Lisp checker

The checker needs something to check, really…
Merge branch 'master' into unit-tests

* master:
  Fix arguments of Emacs Lisp checker
  Do not mess up error match data
  Put first checker error on top
  [Fix #57] Guard the definition of fringe bitmaps
  Fix byte compilation warnings
Configure hook before enabling the mode
Make sure that the checker is running
Fix error check
Add missing require
Change into resource directory

Required by Emacs Lisp checker which is very nit-picky about the working
directory.
Add tests for Emacs Lisp