Add StrPack package

This is the first attempt at pushing a scaffolded (via `Pkg.new(); Pkg.pkg_origin(); Pkg.patch()`) package, so it should get a look over.

Notes:
* `hub create` sets a non-public fetch URL for `origin`, which won't work with `Pkg.pkg_origin()`.
* Need to make sure the branching model for `METADATA.jl` is sane; commits directly to `master` (which is tracking `origin/master`) don't work unless they're immediately going to be pushed; pain and suffering results otherwise.

Workflow notes for pull request to METADATA.jl:

```Bash
git branch -b devel
git add -A -- $pkg
git commit -m "Add  $pkg package"
hub fork
git push $ghuser HEAD
hub pull-request
```