Multi contributors support

[François Benaiteau]

Case where X persons add rewards to same issue, does the resolver gets the total?
And if the rewarder wants to split the money to two persons for instance:

@potogold: $50 are set as reward here
@potogold gives $20 to @benjaminwilson 
@potogold gives $20 to @tomcek112 
@potogold: who else do you want to reward?
@potogold @netbe
@potogold: @netbe receives $10.