v0.5.0-pre

1.Options encoding,ignoreMissing,forceAbsolute and missingStamp are removed,crypto should be repalced by algorithm,doCopy is added;
2.Only path starts with '/' could be treated as an absolute path;
3.Relative paths will never be prepended with any prefix strings;
4.Fixed some bugs;
5.Enhance regular expressions that match url(),link,script and img.