carton 0.3.1

It seems arguable that the Emacs formula should be moved to Dupes. If you agree, then feel free to hold off on creating this formula until Emacs has been migrated.

Also, a plain `prefix.install Dir['*']` keeps a lot of junk. Is that a problem? I've included the output of running `brew ls carton`.

```
/usr/local/Cellar/carton/0.3.1/bin/carton
/usr/local/Cellar/carton/0.3.1/Carton
/usr/local/Cellar/carton/0.3.1/carton.el
/usr/local/Cellar/carton/0.3.1/carton.png
/usr/local/Cellar/carton/0.3.1/features/projects/.gitignore
/usr/local/Cellar/carton/0.3.1/features/step-definitions/carton-steps.el
/usr/local/Cellar/carton/0.3.1/features/support/env.el
/usr/local/Cellar/carton/0.3.1/features/ (9 files)
/usr/local/Cellar/carton/0.3.1/go
/usr/local/Cellar/carton/0.3.1/Makefile
/usr/local/Cellar/carton/0.3.1/server/ (6 files)
/usr/local/Cellar/carton/0.3.1/templates/ (3 files)
/usr/local/Cellar/carton/0.3.1/test/super/Carton
/usr/local/Cellar/carton/0.3.1/test/ (4 files)
```

A quick look through the project makes me think that only `bin/carton`, `carton.el`, and `templates/` are necessary to keep.