Scheme interpreter from tutorial

I added test-cases, implemented reader's exercises and polished code a little bit

Compatibility can be tested with online Scheme interpreter

Stack - the build system

Project was created by

• cabal init - creates initial cabal config file
• stack init - creates new stack project, stack.yaml etc.

Selfexplanatory

• stack build
• stack exec schemeinterpreter - this runs scheme repl :-)
• stack test
• stack repl - opens haskell repl