[ANet] Corrected use of money protocol and examples

[oyeb]

• Adds a new Response field: authorization.
  • It is set to ["transactionResponse"]["transId"]
• Uses Gringotts.Money.to_string instead of converting to lossy Float
• doc examples updated (authorize, capture, purchase)
• Improved all docs, http links and made most lines fit 80 columns
• Ran the elixir 1.6 formatter
  • Used the ~s sigil in mocks
  • Also removed an invisible Unicode codepoint from mock strings

Fixes #90 and Fixes #91