amberc: fix output of 'amberc --help'
amberc.js: check amber_dir in constructor
amberc.js: support multiple library directories
amberc.js: move handling of amber_dir/js and amber_dir/support into AmberC.main()
amberc.js: remove special handling of files in $AMBER/support
amberc: add -L flag to specify additional library directories
grunt-amberc.js: add library_dirs parameter to 'options' which can be used to specify additional library locations
amberc: remove obsolete 'amber_dir' parameter from createDefaults()
Gruntfile.js: remove @ for handling of files in /support
Gruntfile.js: remove obsolete target
Gruntfile: remove yet another obsolete target (amber_compiler)
Merge pull request #700 from mkroehnert/compiler

Compilerflag for specifying js library search directories