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.
:+1: for the documentation, but it is kind of hard to skim through.

Something like http://sphinxcontrib-napoleon.readthedocs.org/en/latest/example_google.html may help.

Since the method signature itself doesn't define the args, it may be easier to read in a format of:
```
auth_msg: A message ...
default_file: A file to use...
```