Updated shape to use style method

Hi again all!

This one involved a little more tweaking than the other ones. It looks like the configuration specs were using Shape (randomly?) so I had to update them to not look for a style hash since shape doesn't use it.

Tests pass and everything else was straight forward so I think this is ready to go. 

PS. I'll merge this (and others) after at least one reviewer gives me the go ahead as per (1) [here](https://github.com/shoes/shoes4/wiki/Merging-a-Pull-Request).
OK so I tried to mimic what color does with a small improvement. 

Right now color uses a sum to compare colors, but the sum is not unique. I notice that @PragTob addressed this in #692 but I guess I don't understand why the `less_or_greater_than` method still uses a sum :blush:.

So in my addition I just bumped the rgb values to digits. For example 12, 128, 5, 0.5 will become 12128005.5 which really does a very different comparison than the original sum, but still puts white > black.

This addresses the issue just fine (now != works as expected) but when I try this simple sample 
```ruby
Shoes.app do
  g1 = gradient(green, orange)
  g2 = gradient(green, red)
  para g1 > g2
end
```
I get
```
NoMethodError: undefined method `>' for (Shoes::Gradient:0x00000fa0 rgb(0, 128, 0)->rgb(255, 165, 0)):Shoes::Gradient
```
What gives?