v0.2.0-Complex, Images, Code clean up

Main new features

• Full Native Complex Number and Complex tensor support.
• Opening images as Ndarr.
• Saving Ndarr as images in multiple formats.
• Activation functions for Ndarr<T: Float,R>.
• Scan operation.
• Num tensor operations: max, min, sum, etc.
• Activation functions.

Changelog

• Code clean up.
• Implement From instead of Into trait.
• Float trait for Trig operations.
• Bug fix in scalar operations.
• Remove unnecessary Traits.
• Complex module.
• de_slice function.
• Scan operations.
• Singed tensor operations.
• README examples.
• Implementing sum operation for Ndarr.
• Hermitian transpose.
• Opening images and Ndarr.
• Implementing saving as RGB image for Ndarr<u8,3>.
• Implementing saving as RGB image for Ndarr<f32,3>.
• Implementing saving as Luma image for Ndarr<f32,2>.
• Implementing saving as Luma image for Ndarr<u8,2>.
• Activation functions: sigmoid, relu, leaky_relu, softmax

##Contributors
@S-Erik @JErnestoMtz