"Soft" pencil down of coding. Begin to write documentaion

Logic caching system is at state of soft pencil down. This means I expect only commits with a javadoc.

My next step is writing documentation and adding it to the openmrs`s wiki.

The documentation will include structure of the caching system, description in details of classes and interfaces user needs to use caching system, code samples, links to different resources.

If some else documentation is needed please add a comment.

I have only one opened issue to add patch of openmrs-core, because of some small changes like adding Serializable to some org.openmrs.logoc.* classes and change ehcache library to the latest version. I plan to create ticket for this.