Merge branch 'patch-1'
Try to clarify as much as possible

* Give a better overview (so people know what they are getting into)
* Make section on primitive types much more focused
* Add additional information about how each feature relates to typed
languages
Add missing commas
Clarify what a record is
Stop using the term "type literals". Use "constant" which is used earlier.
Add another note about what typed json can do
make list of supported things more comprehensive
Fixes based on discussion with @Gozala
Merge pull request #7 from evancz/master

first pass of revisions, mainly trying to clarify and clean up