Adds prefix property on Configuration

Adds "prefix" property to Configuration for carrying the original prefix from
which it was detached from the former container Configuration.
Removed primary constructor default prefix argument

Added secondary constructor and companion object
apply method for API backward compatibility.
Merge pull request #15 from plalloni/master

Detached configuration prefix memoization
Fix typo in ConfigurationSpec
Fix Travis badge
Merge pull request #17 from jvirtanen/fixes/travis-badge

Fix Travis badge
Merge pull request #18 from jvirtanen/fixes/typos

Fix typo in ConfigurationSpec
Add 'Configuration#detachAll'

For each unique prefix in the configuration, it produces a new
configuration containing the values whose keys have the common
prefix. It returns a map from prefixes to configurations.

This is useful in the following scenario:

  accounts {
    alice {
      group: admins
      name:  Alice
    }
    bob {
      group: users
      name:  Bob
    }
  }

Here the account identifiers, 'alice' and 'bob', should obviously
not be hard-coded into the application. 'Configuration#detachAll'
on the 'accounts' sub-configuration provides a convenient discovery
mechanism for the configured accounts.
Merge pull request #19 from jvirtanen/features/detach-by-unique-prefixes

Add 'Configuration#detachAll'
Allow to parse "yes/no" into a Boolean
Merge pull request #20 from yurkom/master

Allow to parse "yes/no" into a Boolean
Merge branch 'master' into scala2.10
Dropped scala 2.8 support; cross-building for scala 2.9 and scala 2.10