YAML configuration file reader with basic variable interpolation.

Requires PyYAML <http://pyyaml.org/wiki/PyYAML>

Example
=================

/etc/dummy_config.yaml

main:
    name: 'Napoleon'
    age: 15
    skills: ['Ninja', 'Dancing', 'Nunchucks', $default_skills]
    net_worth: $10


>>> from yamlconfig import YamlConfig

>>> defaults = {'default_skills': 'KickBall'}

>>> config = YamlConfig('/etc/dummy_config.yaml', defaults)

>>> config['main']['name']
'Napoleon'

>>> type(config['main']['name'])
<class 'str'>

>>> config['main']['age']
15

>>> type(config['main']['age'])
<class 'int'>

>>> config['main']['skills']
['Ninja', 'Dancing', 'Nunchucks', 'KickBall']

>>> type(config['main']['skills'])
<class 'list'>

>>> config['main']['net_worth']
'$10'

>>> type(config['main']['net_worth'])
<class 'str'>

