Drop Ruby 1.9.2 support
Turn all doc to tomdoc format
Add dev dependency: rspec
Add randomization
Change rspec options
Add new dev dependencies
Improve metrics tasks
Ruby 1.9.3 as a minimum version
Remove reference to Ruby 1.9.2
Add a «Contributing» section
Travis CI: change 2.1.0 to 2.1

There was a bug on Travis CI which cannot install binary for Ruby 2.1.0.
Bump version 0.10.0