Flogger 0.5

• Explicitly allow an array containing null objects in logVarargs(). (0805f96)
• Adding "callerOf(Class<?>)" to LogSites. (91d4388)
• Adding initial common API for per-request logging configuration support (implementation to follow). (e0493d7)
• Add support for '(' flag in Flogger for negative numbers (df6dfe5)
• Minor code tidying of the log4j backend. (e1374b4)
• Add support for log4j2 as a backend. (356778a)
• 71f6083:
    - Promoting the "with()" method from GoogleLogger to FluentLogger.
      - This is useful to piggyback semantic information about the log statement into For example, identifying special log statements which should be handled differently (e.g. sent to a different log file).