Merge pull request #1 from mrshu/master

Added day/hour heatmap
formatting
build tasks
Readme changed
Readme changed
Fixed yValue usage

Previously d.frequency was hardcoded in an equation. If you used some other `yValue`, it would return NaN which is not very much drawable.
Merge pull request #2 from mrshu/patch-1

Fixed yValue usage
updated readme
Update heatmap.html

Add option time format and click event on rect elements
Update dayhourheatmap.js

Add option time format and click event on rect elements
modified time_format
Added value tracking on hover
Added mouseValue option