GROOVY-6268: Design patterns in Groovy

Some qestions and comments:
- Broken local links (I cant find these sections in new doc):
 - <<_refactoring_bwith_groovy,Refactoring with Groovy>>.
 - <<_replace_inheritance_with_delegation,Replace Inheritance with Delegation>>.
 - <<_model_based_testing_using_modeljunit,Model-based testing using ModelJUnit>>
- Broken external links (The webpage is not available):
 - http://www.cmcrossroads.com/bradapp/docs/pizza-inv.html [Pizza Inversion - a Pattern for Efficient Resource Consumption].
 - http://scala.sygneca.com/patterns/loan [Loan my Resource] (I replaced to https://wiki.scala-lang.org/display/SYGN/Loan).
 - http://wiki.rubygarden.org/Ruby/page/show/NullObjectPattern [this].
 - http://wiki.rubygarden.org/Ruby/page/show/ProxyPattern [Ruby example].
 - http://wiki.rubygarden.org/Ruby/page/show/StatePattern [Ruby Example].
 - http://wiki.rubygarden.org/Ruby/page/show/VisitorPattern [this].
- I can't reproduce table with block codes and images from http://groovy.codehaus.org/Flyweight+Pattern.
- I got some warnings with leveloffset markup when assembleAsciidoc. I don't understand why.