Fix for issue 54

Moved keywords to this page and removed from DataStructures page since it doesn't make sense till its used. Will fix Issue #54

add more examples of data structures in collections of collections

Put the examples of map functions inline with the descriptions, easier to read through without having to jump around.

When discussing with Norman and reviewing i removed the bit about commas being whitespace and could be used to separate key/value pairs in maps. If someone is having problems understanding and have done programming in languages that do separate with commas then we can mention it but I don't think it should be put in the curriculum. [Styleguide](https://github.com/bbatsov/clojure-style-guide) says not to use commas.

Exercises, added links to docs and more detail to hints as I at first had some problems figuring it out myself.
Introducing the map function in a section on the map data structure may cause confusion.