Add set binding

[messense]

TODO:

• frozenset?
• add more tests

Ref #2

Currently this project is a little hard to get involved because of lacking development guide docs.

[messense]

I am not sure how to implement:

• set iterator
• set union, issuperset, etc. methods.

[fafhrd91]

I think PyIterator instance is fine

[fafhrd91]

lgtm on implementation

do you want to implement iter()?

[messense]

Switched Travis CI distribution to trusty.

https://blog.travis-ci.com/2017-04-17-precise-EOL

[messense]

What do you think if we change this to:

pub fn new<T: ToPythonObject>(py: Python: elements: &[T]) -> PySet {}

so that we can do:

let set = PySet::new(py, &[1, 2, 3]);

instead of

let set = PySet::new(py, &[1.to_py_object(py).into_object()]);

[fafhrd91]

I think, this is very good idea

[messense]

But other things like PyList still uses pub fn new(py: Python, elements: &[PyObject]) -> PyList, I guess we should do this in a separate PR to do them all.

[fafhrd91]

I think you should have write access to repo. this kind of change you can just commit.

[messense]

OK, I'll merge this then do other things.