Feature: `config.truthy` helper

[grimen]

Useful for less verbose environment flag parsing.

Example:

config.truthy(None) # => False
config.truthy(False) # => False
config.truthy(0) # => False
config.truthy("0") # => False
config.truthy("false") # => False
config.truthy("False") # => False
config.truthy("FALSE") # => False
config.truthy("no") # => False # e.g. YAML
config.truthy("No") # => False # e.g. YAML
config.truthy("NO") # => False # e.g. YAML
config.truthy("") # => False
config.truthy("nil") # => False
config.truthy("null") # => False

config.truthy(True) # => True
config.truthy(1) # => True
config.truthy("1") # => True
config.truthy("true") # => True
config.truthy("True") # => True
config.truthy("TRUE") # => True
config.truthy("yes") # => True # e.g. YAML
config.truthy("Yes") # => True # e.g. YAML
config.truthy("YES") # => True # e.g. YAML
config.truthy({}) # => True
config.truthy([]) # => True