slider draw parameter is now a d3 selection

- Also fixed the mismatch between the newValue in the changedValue event and the getValue method.
- Many comment updates
small text change
Merge pull request #67 from mlippert/sliders

slider draw parameter is now a d3 selection
Merge remote-tracking branch 'upstream/master' into seann
Merge pull request #68 from seannives/seann

Seann