From/To/AsPrimitive and NumCast for Complex<T>

[termoshtt]

I added a submodule cast which defines four traits in num-traits::cast:

• ToPrimitive::to_xxx returns None if im is non-zero
• FromPrimitive::from_xxx(a) returns Complex { re: T::from_xxx(a), im: T::zero() }
• AsPrimitive drops the imaginary part of complex
• NumCast is same as ToPrimitive

[termoshtt]

Fix 1.15.0 case

[termoshtt]

Thanks review. I fixed them.

[cuviper]

Thanks!

bors r+

[bors[bot]]

Build succeeded

• continuous-integration/travis-ci/push

[termoshtt]

Could you release 0.2.1? or any release schedule?

[cuviper]

Could you release 0.2.1?

Done!