Allow filesystem to work on different pins

[gfwilliams]

Something like:

require('fs').connect(SPI1,cs);

Probably makes more sense than E.connectSD as that's how everything else is done

[gfwilliams]

There actually is, it's just hard to find: http://www.espruino.com/Reference#l_E_connectSDCard

I'll add a bug in EspruinoDocs - a general FS documentation page is needed badly anyway.