Merge pull request #16 from brianhanifin/feature/cache

Gzip / Caching Improvements
Adding retrospective predictor. When viewing historical data, time and sg become stale via a strikethrough. Focus now line is fixed at 30 minutes less of the extent and if sg if not within a tolerance of time, sg is displayed as "---".
Update client.js
Merge pull request #18 from nightscout/retrospective-prediction

Adding retrospective predictor. When viewing historical data, time and s...
Merge pull request #2 from nightscout/master

Merge retrospective-prediction