Further localize brush related code.
The proper way to remove properties is using delete.
Add support for combining brushed axes with OR

Up to know, brushed axes where combined using AND, meaning: a line must go
through all brushes to be inside the selection.

This commit adds the possibility to do OR combining, meaning: a line must
go through at least one brush to be inside the selection.

Usage:

d3.parcoords(div)
  .brushMode("1D-axes")
  .brushPredicate("OR")
Fix a typo.
Remove unnecessary semi-colon
Update d3.parcoords.js
Add OR filter combination to the brushing example.
Make some tests slightly more specific.
Remove debug statement.
Update d3.parcoords.js
Extend the brush example to demo all brush related options.

It now demonstrates how to switch between various brushing mode. It also
demonstrates the difference between AND and OR combinations of filtering.