Move Schema to separate file and add User entity

See #264

git-svn-id: http://gsoc.svn.wordpress.org/2013/rmccue/trunk@1983 f69abe3c-2ee2-4550-9a6d-17bd458115be
Rework the entire design specification

This separates Documents from Entities and more rigorously describes the data
returned from the API.

See #264

git-svn-id: http://gsoc.svn.wordpress.org/2013/rmccue/trunk@1984 f69abe3c-2ee2-4550-9a6d-17bd458115be
Ensure we use consistent JSON terminology

See #264

git-svn-id: http://gsoc.svn.wordpress.org/2013/rmccue/trunk@1985 f69abe3c-2ee2-4550-9a6d-17bd458115be
Add some whitespace for plain text readability

git-svn-id: http://gsoc.svn.wordpress.org/2013/rmccue/trunk@1986 f69abe3c-2ee2-4550-9a6d-17bd458115be
Note that ABNF specifies literals as case insensitive

See #264

git-svn-id: http://gsoc.svn.wordpress.org/2013/rmccue/trunk@1987 f69abe3c-2ee2-4550-9a6d-17bd458115be
Use / instead of | in ABNF

As per the ABNF specification used in this document, / should be used for
alternatives rather than |

See #264

git-svn-id: http://gsoc.svn.wordpress.org/2013/rmccue/trunk@1988 f69abe3c-2ee2-4550-9a6d-17bd458115be