Extended the user guide regarding reloading.

Started a chapter about automatic reloading.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1594691 13f79535-47bb-0310-9956-ffa450edef68
Added missing Javadoc for a parameter.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1594692 13f79535-47bb-0310-9956-ffa450edef68
ReloadingFileBasedConfigurationBuilder now overrides configure().

The return type is overloaded to enable method chaining with correct return
types.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1594693 13f79535-47bb-0310-9956-ffa450edef68