Added Crosshair

[binoculars]

Crosshair (or more formally, reticle)
https://en.wikipedia.org/wiki/Reticle. Put it in plugins, because it
seems like an appropriate spot for it.

Made this for my pet project. It would be nice to get it in the main repo.

[ericdrowell]

This is awesome! However, this is more appropriate as a 3rd party plugin. KineticJS is made up of:

1. core shapes
2. KineticJS managed plugins
3. 3rd party plugins

A cross hair would fit much better as a 3rd party plugin. Would it be possible for you to create a github repo for this, and I can link to it from KineticJS? I will be putting together a plugin gallery soon.

Thanks!

[binoculars]

Definitely. I started https://github.com/binoculars/KineticJS-plugins

I tried to keep it in line with the structure of your main repo.