added claim check + bitmap

[FreezyEx]

Credits: Uniswap MerkleDistributor

Gas Snapshot:

test_claim() (gas: -113926 (-16.069%))  
test_prove() (gas: -646558 (-60.497%))

[merklejerk]

Ooooh thanks for bringing my attention to the missing hasClaimed check! I patched it in main. 😓
But I think this version doesn't address the vulnerability since you can still could claim multiple times for a member just by using a different index to the bitmap. I also think the bitmap is a bit distracting from the pattern being illustrated because I think bitmaps are cool enough to deserve their own guide. If you want to write one, I'd be very interested.

[FreezyEx]

My bad, I forgot to add the index parameter to the generation of the tree and in the prove phase.