Upgrade to rspec 3
Upgrade .rspec and spec_helper to v3 standard files.
Cleanup warning issues after transpec update
Upgrade Travis for newer rubies.
Set required Ruby version in gemspec
Changed README badges to .svg
Fix issue with hex_dump on Ruby 2.0
Fix issue with warnings generated for #duplicates on Ruby 2.1

Ruby 2.1 complains when reject is called on a Hash with a
default value.  Switching to select doesn't complain.
See also https://bugs.ruby-lang.org/issues/9275