package.json: add es6-promise to dependencies
amberc.js: remove obsolete require('exec') and require('util')
amberc.js: require('Promise')
amberc.js: rename check_configuration_ok() to check_configuration() which now returns a Promise
amberc.js: compose_js_files() returns a Promise
amberc.js: verify() returns a Promise.all() object
amberc.js: category_export() returns Promise.all() object
amberc.js: remove obsolete async_map()

replaced by Promise.all()
amberc.js: use Promises for compile step

split the compile function in two separate phases
readFiles() + compile()
amberc.js: create_compiler() now uses Promises
amberc.js: turn resolve_js() into normal function
amberc.js: use Promises for resolve_kernel() and resolve_compiler()
amberc.js: remove obsolete always_resolve() function
amberc.js: collect_js_files now returns a Promise
amberc.js: collect_st_files now returns a Promise
amberc.js: collect_files(), collect_st_files(), collect_js_files() now take only configuration as parameter
amberc.js: merge resolve_libraries() into collect_files()
amberc.js: finally remove the Combo construct
amberc.js: merge collect_files() into AmberC.main()
amberc.js: remove self.defaults reference