injectedlogger: fix possible call on nil value
injectedlogger: allow logger to be default while adding extra params
injectedlogger: add after_injection hook
README: add simple after_injection example
logger: support logging with blocks

This allows us to call logger with expensive computations like:

InjectedLogger::Logger.info do
  md5 = DigestMD5(somebigchunkofdata)
  "MD5 #{md5}
end
logger: add support for :log with blocks
injectedlogger: release 0.0.6