D3 version 4 tooltip

Major breaking release -- supports version 4 of D3 from this version forward.

CSS addtion/Bug fix

Added point-events 'none' to the root (caused blocking issues while hidden)
Added 'kodama-tooltip' class for CSS styling (for those who wish to use it)

Bug fix release

1. Target accepts jquery and d3 selections as well as nodes now (uses first node found)
2. Setters properly handle falsey values (was not accepting e.g. distance 0)
3. Gravity center positioning now works as intended

Target DOM nodes

'target' and 'by' methods now allow tooltips to reference and lock on any node.
'white_wolf' theme added for testing and reference.

Tooltips -- launch features

1.1.2

Update package.json