Fixed issues with schema

The schema looks really good, but there are a few issues. 

1. `#/bio/profiles` was limited to `twitter` and `github`
2. There were not enough restriction on the format, so any JSON file would validate against this schema.

I've added tests for this schema here http://schemastore.org/test/ against two JSON resume files. The official resume file from this repo and the example from your website (thomasdavis.json). Notice that the thomasdavis.json is slightly modified. It didn't actually validate against the schema.