Add 'brew bundle' path support

As we talked about in #24107, it would be helpful to be able to use a custom path with `brew bundle`. I changed the error message to use the same structure as `brew uninstall` errors, so that errors are more useful.

**Old:**
> Cannot find Brewfile

**New:**
>Error: No such Brewfile: /path/to/non/existent/file/or/directory

I've also copied the usage notes to this issue so that it's easier to read.

---


## brew-bundle.rb
Looks for a Brewfile and runs each line as a brew command.

**Usage:** `brew bundle [path]`

```
brew bundle              # Looks for "./brewfile"
brew bundle path/to/dir  # Looks for "./path/to/dir/brewfile"
brew bundle path/to/file # Looks for "./path/to/file"
```

For example, given a Brewfile with the following contents:

```
tap foo/bar
install spark
```

Running `brew bundle` will run the commands `brew tap foo/bar` and `brew install spark`.