GROOVY-6295 escaping angle brackets in GroovyDoc @code and @literal tags
Merge pull request #237 from darxriggs/groovydoc-code-and-literal

GROOVY-6295 escaping angle brackets in GroovyDoc @code and @literal tags
Gradle build tweaks:
   * replace .add with .create for task creation
   * fix dependency to ASM in utils.gradle
   * replace trick to compile Groovy with invokedynamic support with direct Gradle support