Bitcoin pdf spanish translation

First version of the Bitcoin paper translated to Spanish (Latin American). 

Multiple modifications were made on the document after the feedback of several members of #bitcoin-es. 

There's still more work to be done, but this is a lot better than taking Spanish readers to the English version of the paper. 

Not sure where else to put the pdf for now except at the same level as the bitcoin.pdf, @gavinandresen said to submit the pull request and then he'd move it elsewhere if necessary.

Cheers