[Added] Spare piece counts functionality

[sanjaynishad]

I have added a Config property spareCounts.
spareCounts will accept a string "default" or a valid JSON object.
e.g.
var cfg = { spareCounts: 'default' }
or
var cfg = { spareCounts: { 'wK':0, 'wQ':0, 'wR':0, 'wB':0, 'wN':2, 'wP':1, 'bK':0, 'bQ':0, 'bR':0, 'bB':0, 'bN':0, 'bP':0 } }

Updated: see the image http://www.sanjaynishad.com/files/02f0b9f6-356a-4442-b797-29908674e250.png

[sanjaynishad]

hey @oakmac
may I know, why this PR isn't merged yet?

[oakmac]

The honest answer is that I haven't looked at it in depth.

I'm not sure how this functionality would effect the API.

[sanjaynishad]

okay, when are you going to look in depth? :)