support symlink field in 'files'

symlink intends to make symbolic links for local directories or files

Enyo-DCO-1.1-Signed-off-by Junil Kim <logyourself@gmail.com>
addressed travis-ci warning
indent
addressed travis-ci warning
Merge pull request #15 from enyojs/ENYO-4091

support symlink field in 'files'