Nested namespaces

[mistersourcerer]

This PR adds the ability to create a settings class with a nested namespace, so the "base hash" can be fetched from inside some yaml key.

  # /some/file/here.yml
  professional:
    preferences:
      order: desc
  client:
    prefs:
      order: asc

  class ProfessionalPreferences < Settingslogic
    source "/some/file/here.yml"
    namespace "professional.preferences"
  end

  >> ProfessionalPreferences.order
  => "desc"

[zhouguangming]

+1