Merge pull request #3 from froj/master

Feature: Resistance tolerance taken in account
Remove dependency on numpy

Numpy is a pretty heavy dependency for a script like that and was not
used in the main loop (classic list() instead).
Remove numpy dependency from README
Merge pull request #4 from antoinealb/remove-numpy

Remove dependency on numpy
suppressed redundancies & corrected indentation
readme completed and corrected
Add E series support for resistor values
Less restrictive choice of resistor value series
print Vout