mean_stdv refactor

[JoFrhwld]

The code in mean_stdv() should be refactored with numpy

FAVE/fave/extractFormants.py

Line 1068 in ce2c5cf

def mean_stdv(valuelist):

[chrisbrickhouse]

Good first issue:

• Write a test for the current output with lots of test cases
• Remove existing code and replace with numpy calls
• Ensure that the tests still pass, proving that the function output is identical

[DerMoehre]

Hi,
I wrote a test for testing the existing code in extractFormants.py
It works locally, but fails if I try to create a pull request here on GitHub and somehow, it wants to add these code to the open pull request "Added badges to README". Is there a way to create another PR?

[JoFrhwld]

Closed with #84