Even more helpers

• fn shorthand for the function type
• typify.wrap to typify modules
• istanbul code covarage as part of the test suite
• typify.adt helper for specifying abstract data types -like structures
• infinity, ninfinity and nan literals
• unified implementation of typify.type, typify.alias and typify.record.
  • The latter two will be deprecated in 0.3.0 and removed in 0.4.0