Scattered corrections and improvements, and tests for python and julia versions

I have added a number of scattered corrections and improvements in both versions, including updates in the Readme.md files. I have also included tests in julia and made as compatible as possible with those in python. Still, there are some things to check.
Why did you change `Real` to `Number`? We do not want to allow complex numbers inside these intervals. (That would be a different interval class I believe.)