updated tests/, tqdm removed & release setup
tests updated to improve code coverage when retrieving data from intervals over 20 years
removed return statements that are lines missed because previous checks avoid them
tqdm package removed as it is not necessary and it can also be annoying (even though it can be useful when testing functions)
setup.py, requirements.txtm README.md and .travis.yml updated to fit new release version 0.8.4.8
additionally notebooks/ have been removed as improves, proposals and changes tests need to be done in another repo or branch so as no to interfere in investpy package
