Go Data Frames supporting np like behaviours

A very limited implementation of np like data frames, built to support the project

https://github.com/mdcfrancis/gomnist1d

To create the data set it is important the the random number generation is stable and the code is a fairly close match to the original mnist1d code style.

No parts of the original numpy are used in this code base.

• Implements a simplified version of NpArray and NpStack, including many helper methods.
• Only supports one dimensional arrays and stacks of frames.
• Uses the same random number generator as the original code from numpy (golang impl).
• Implements np.RandChoice an extensions to randomkit to exactly match intn from numpy.

References

• https://github.com/montanaflynn/stats : stats library is lightly used but allows for additional support if needed.
• https://github.com/pa-m/randomkit : without this library the random number generation would not match.