added a config parameter that allow specification of filename, defaults to assets if no name is specified
Added option to specify custom targets
Added option to manually specify target files and updated readme for the new options
added default to '{}' in order to avoid undefined error when option is not supplied
added support for multi task

updated readme for new multitask config options
added a sanity check before trying to write merged file, since files can have a custom destination we may endup having nothing to merge and writing an empty file
fixing merge
fixing readme indentation
updated version on package.json