Add input size check to update() method

[VictorColomb]

In response to #18.

Add a check on the input size of the Blake2b.prototope.update() method.

blake2b-wasm/index.js

Line 82 in 0359a9b

assert(input.length + head <= 65536000, 'input + head must be of size 65,536,000 or less')

Reason

The WebAssembly instance memory is limited to 65,536,000 bytes (64 * 1,000 KiB) because of the following:

blake2b-wasm/blake2b.wat

Line 3 in 7d8efa4

(memory (export "memory") 10 1000)

Therefore, the memory can only grow to this size, and the update() method fails when input.length + head > 65536000.

[VictorColomb]

Ping @mafintosh