Changed the package structure to better reflect the different modules of the library. All client related code now lives in the client package, server related APIs in server with their respective WebMVC and WebFlux implementations in sub-packages.
Added migration script to allow users to easily migrate to the new structure and added reference documentation section on the migration.
Traversons built in defaulting to HAL HttpMessageConverters and LinkDiscoverer implementation now caused a cyclic relationship between the client and mediatype.hal packages. This has be fixed by looking up the defaults via a SpringFactories interface.
