Sigpro

Features

* Frequency primitive - [Issue 60](https://github.com/sintel-dev/SigPro/pull/60)

Features
* Demo Notebooks for Pipeline usage - [Issue 55](https://github.com/sintel-dev/SigPro/issues/55) by andyx13
* Added `contributing_primitive` and `basic_primitives` module to assist with new primitive creation/usage - [Issue 54](https://github.com/sintel-dev/SigPro/issues/54) by andyx13
* Incorrect classification for stft.json and stft_real.json - [Issue 53](https://github.com/sintel-dev/SigPro/issues/53) by andyx13
* Support for more complex pipeline architectures - [Issue 52](https://github.com/sintel-dev/SigPro/issues/52) by andyx13
* Update primitive interfaces - [Issue 51](https://github.com/sintel-dev/SigPro/issues/51) by andyx13
* Syntax for pipeline creation - [Issue 41](https://github.com/sintel-dev/SigPro/issues/41) by andyx13
* Load demo dataset at random index - [Issue 35](https://github.com/sintel-dev/SigPro/issues/35) by andyx13

Features
* Python version update - [Issue 44](https://github.com/sintel-dev/SigPro/issues/44) by andyx13
* Add demo notebook and per-primitive documentation - [Issue 47](https://github.com/sintel-dev/SigPro/issues/47) by andyx13

Features
* Accepting single value data frame format - [Issue 36](https://github.com/sintel-dev/SigPro/issues/36) by frances-h sarahmish
* Update demos - [Issue 26](https://github.com/sintel-dev/SigPro/pull/26) by frances-h

Features
* Rework SigPro to be class based

Features
* Add `process_signals` function to take a collection of primitives and create features for the given data.