Adds configurable key bindings using rc.

See [documentation](https://github.com/dominictarr/rc)

The appname is 'vimdebug' and key bindings are under vim.keys.<command>, e.g.:
`vim.keys.break`.

For example, to configure the add-breakpoint key to <Ctrl-b>

`./lib/vim-inspector.js --vim.keys.break="C-b"`

or a `~/.vimdebugrc` containing:

```json
{
  "vim": {
    "keys": {
      "break": "C-b"
    }
  }
  // vim: set ft=json:
}
```

Closes #13.
Increases setTimeout delay before dc.connect to 300ms.
Makes debugger port variable, uses --debugger.port=<String|Number>.
Places debugger output on a new line and prefixes each individual line with 'out >'.
Merge pull request #20 from jbnicolai/issue/14

Start the debugger in a child process if a script path is given.