config files

There are too many arguments to pass to `Qdb` to make setting breakpoints fast and simple.

This adds a `.qdb` file parser and scheme. The `QdbConfig` is a namedtuple that holds all the arguments to be passed to Qdb.

It checks for config files in:
- cwd
- `$HOME`
- Any files explicitly given.

`QdbConfig`s can also be constructed from a dict to make setting custom configs programatically simple.
Any thoughts about just picking one?

For what it's worth, my default assumption of behavior would be any kwargs would overwrite the file config.