Hadoop DFS support

* Introduced a hadoop command enforcing user config and hadoop-ext
  configuration files (hadoop.xml) that calls the hadoop runner
* Introduced the following commands and runners that utilize the hadoop
  runner (to work against the DFS): mktemp, withtmpdir and rm
* Support for hadoop_confs in Hadupils::Extensions
* Introduced Hadupils::Extensions::Dfs::TmpFile
* Introduced Hadupils::Hacks module for String Refinements
* (self.randcase)
  for Ruby 2+ and Monkey Patching for the String class for Ruby < 2.0
* Some refactoring and fixed a bug with the specs for Mac OS X
* Tweaked old unit tests and added new ones for the new features
* Updated the README with examples
* Bumped version to 0.5.0