For numeric code, comparing to pure python makes no sense, since people use numpy+numba to do that. Is julia much much faster than numba? I don't think so :)
So wonderful job! My favourite feature is providing a whole development environment with docker, it can save me a lot of time, and make me focus the source code.
For #15, if the number of elements is large, the speed will be slower than we expected, since maxx function is writren in pure python.
But in my experience, it is much faster than for loop in pure python.