0.18.8

Changes from 0.18.5
* (ethash, kawpow, progpow) Reduce GPU memory consumption (by ~6MB)
* Add etchash algorithm for upcoming ETC fork
* Cache DAG for epoch 0 when mining ETH+ZIL (run with --extra-dag-epoch 0 parameter)

Bug fixes:
* (ethash) kernels 4 and 5 generate incorrect shares if DAG size > 4GB (e.g. when mining ETC)
* (ethash) out of memory error in "zombie" mode
* worker parameter is ignored if placed under pools section in a config file
* Various web UI fixes
* The miner now reports hashrate every 2 seconds in benchmark mode