new method for press_keys

This allows for multiple key presses a bit easier than currently. Eg.
k.press_keys(['Command','shift','3'])
added line re: press_keys

with example for windows and mac
a hello world example with pyKeyboard

I’m hoping this explains the methods a bit better.
typos
Changes to the consistency lines..

I *think* the dir(k) function isn’t working on windows or mac- hence
changing this. This got me stumped for ages..
typos to readme
Merge pull request #44 from willwade/master

new method for press_keys