Add @see links.
Rename Log4j 2.0 -> Log4j 2 in javadoc.
Add getCallerClass(Class) method.

  - Can be used when the FQCN is known in advance and is an
  accessible class at compile time.
Add AbstractLoggerAdapter.getContext(Class).

  - Provides a useful method for implementing getContext() when
  combined with ReflectionUtil.
Simplify log4j-jul LoggerAdapter implementation.
Simplify log4j-jcl LoggerAdapter implementation.
Simplify log4j-slf4j-impl LoggerAdapter implementation.