Collect the requirements for processors interactions

[ykryshchuk]

Here we will collect all requirements for contract between different configuration processors.

The result of the issue should be a new Processors Contract page on project's wiki.

[ykryshchuk]

Added a page https://github.com/BAXTER-IT/yurconf/wiki/Sharing-Configuration-Processors-Resources

[ykryshchuk]

In general:

• the custom configuration processor should be able to reuse other processors classes. This is achieved by using the ProcessorsClassLoader
• a custom processor should be able to use XSLs provided by other processors. This is done by org.yurconf.processor.impl.YurconfUriResolver
• a processor should be able to access the files from its own configuration repository or from other products repositories (to share data). Implemented by YurconfUriResolver.

See also https://github.com/BAXTER-IT/yurconf/wiki/Yurconf-URI-Resolver.