Added warranty information to the Idris Repl.

Added REPL command: `:w`, `:warranty`.

This command displays the warranty information governing the use of `Idris`. This information comes from the last paragraph of the software license that `Idris` is licensed under.
Modified REPL banner statement.
Merge pull request #1276 from jfdm/warranty-flag

Added warranty information to the Idris Repl.