Update to JSON.NET 4.5r10

Also fix a few failing tests.  I believe the test fixes were unrelated and simply the result of us not running them as often as we should.
Merge pull request #34 from AnalyticalGraphicsInc/Json.NET

Update to JSON.NET 4.5r10
Updated README.md
initial pass of MultiTrack support.
tests and tweaks for GxMultiTrack.
function rename for consistency.
updates based on code review.
Merge pull request #37 from AnalyticalGraphicsInc/MultiTrack

Multi track support
Fixed JSON Schema Validator error
Merge pull request #38 from AnalyticalGraphicsInc/jsv

Fixed JSON Schema Validator error
Merge branch 'master' of https://github.com/gbeatty/czml-writer into videoMaterial