add contribution guide
Merge pull request #25 from gurugray/contibute

add contribution guide
bump version
remove unneeded marker on creating node

marker allready added on next tick
remove unneeded calculations on creating node

there are allready calculated on next tick
stop drawing empty text lables

I have splited array of nodes to draw labled separately from not labled.
simplify calculation of new node coordinates
set relative coordinates

  * set new constant for node radius.
  * calculate coordinates od texts on it.
simplify coorditnates calculation
remove unneeded refY on marker
style guide

I'm forgeting to lint :(
upgrade d3js