Update documentation and make unmapping fail silently

Hi,

I like your idea of disabling h,j,k,l etc to break your habits very much :)
However, there are 2 things that I changed:

* The message in HardMode says

    "VIM: hard Mode [ :Easy to exit ]"

That command does not (longer) exist, I changed it to

    "VIM: hard Mode [ ':call EasyMode()' to exit]"

* If you press <leader>h while in EasyMode all unmaps fail

So I added "silent!" in front of every unmapping to make it fail silently if no such mapping exists

Regards,
Markus