Add basic test for Project().

Standing by [my promise](https://github.com/Jragonmiris/mathgl/issues/2#issuecomment-33110553) to deliver _something_, even if it's not the best test case (taken from an ortho projection).

But it's a starting point that's better  than no test, and it can be made better.

```
mathgl $ go test .
ok  	_/Users/Dmitri/Desktop/mathgl	0.014s
```