Added Ripl::History::HISTORY_FILE.
Use https:// links to github.
Link to the GitHub READMEs.
Link to ronin-ruby.github.io.
Use fixed width fond for filenames, commands, ruby code.
Consistent spacing.
Try to keep text within 80 columns.
Link to ripl-irb.
Merge pull request #34 from postmodern/readme-formatting

Readme formatting