#3 Add support for *.tar or *.zip (.gz) requirements

On mac you must do `brew install wget` also.  Currently the type is still 'vcs', you might want to create a new type and throw this in there for 'archive' types.
can this check happen in the constructor, rather than in resolve? I.e., in the constructor, determine if the type is "git", "hg", or "zip/tar" based on the URL, and then cue off self.type here. This could be a helper function, e.g., "inferURLType"