Use latest stable version of rspec and remove minitest dev dependency
Move test suite assets into spec/assets
Rendering specs now match output with actual expected results

- Add expected assets
- Add match_binary_asset rspec custom matcher
- DRY up rendering specs a little
Upgrade prawn gem to latest stable release 1.0.0

After one change to fix broken formatting of bold table cells, rendered output appears identical to previous expected assets. Test assets have been updated to reflect internal differences due to new prawn gem.
File cleanup.
i18n updates and more.