Add polygonal chain emitter generator

[romadanylchuk]

The functional gives way to generate emitters along some polygonal chain curve.

[andrewstart]

I like what I see here. I did some cleanup, but I have a few changes that I want to make - you are doing a little more math than you need to for interpolation, it looks like it would break if the chain only had one point (like it would if the config was incorrect), and I'd like to make a couple larger changes:

• have an equal chance of spawning at any point on the chain, (currently an equal chance per segment, which means shorter segments will have denser particles)
• support disconnected line segments rather than only one connected line

I have some plans on how to do this, but will be busy next week and didn't want you to think this went unnoticed.

[andrewstart]

Alright, I've done the things that I wanted to do to it - are there any other features that would be easy to add that would hit any potential use cases that we have missed?

[romadanylchuk]

Oh, you have done great work! Actually, it is more then I wanted to do, thank you a lot!