Drop Ruby 1.8 support

Closes #54
Merge pull request #56 from vid-io/cleanup/drop-ruby-18-support

Drop Ruby 1.8 support
Revert "Drop Ruby 1.8 support"

This reverts commit e70c6f68ddf7ec50f43fd04561bb0e99a4fde813.
json is not necessary on Ruby versions that include it in the stdlib
New logo
Center text in logo
Bigger input buffer
Rubocop fixup