Added ConfigurationDecoder interface.

This interface will be used when querying encoded strings from a configuration
file.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1638378 13f79535-47bb-0310-9956-ffa450edef68
Added methods for querying encoded strings to ImmutableConfiguration.

With these methods it is possible to query the values of configuration
properties stored in encoded form. Before they are handed to the calling
application, the values are passed to a ConfigurationDecoder.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1638379 13f79535-47bb-0310-9956-ffa450edef68
Implemented getEncodedString() which expects a ConfigurationDecoder.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1638381 13f79535-47bb-0310-9956-ffa450edef68
Implemented getEncodedString() using a default decoder.

A property for the default decoder was added to AbstractConfiguration.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1638382 13f79535-47bb-0310-9956-ffa450edef68
Extended BasicBuilderProperties by a ConfigurationDecoder property.

It is now possible to set the decoder property via initialization parameters of
a configuration builder.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1638383 13f79535-47bb-0310-9956-ffa450edef68
The configuration decoder is now taken into account when copying basic properties.

A sub combined configuration builder inherits the decoder property from its
parent.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1638384 13f79535-47bb-0310-9956-ffa450edef68
Enhanced user guide regarding access to encoded strings.

A new subsection was added to the "basic features" document.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1638385 13f79535-47bb-0310-9956-ffa450edef68
[CONFIGURATION-565] Updated changes.xml.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1638386 13f79535-47bb-0310-9956-ffa450edef68