HAL spec Link Objects support

(Includes all of https://github.com/mdsol/crichton-dotnet/pull/11 - please merge that one first)

This PR adds full support for the HAL subset of Link Objects as of http://tools.ietf.org/html/draft-kelly-json-hal-06.

```
5.  Link Objects
5.1.  href
5.2.  templated
5.3.  type
5.4.  deprecation
5.5.  name
5.6.  profile
5.7.  title
5.8.  hreflang
```

Support of all these is of course required for Hale support, and is a first step. Next up are the extra amendments to Link Objects in Hale.

@mdsol/hypermedia-team Please review and merge, after merging https://github.com/mdsol/crichton-dotnet/pull/11.