use File.require to find files
use _dependencies to file.lookup
support parse file in dependent package #11
improve code

1. file.filepath -> file.path
2. pass pkg as an argument to lookupFiles
3. imporve debug
file.addDeps/getDeps
improve log spmjs/spm#951
Merge pull request #17 from popomore/parse-file-in-package

解析模块内的文件