moved src/bin/client.rs -> src/bin/client/main.rs

removed overflowing_shr

fixed wrapping ops on latest nightly

Memory management for cache

Implement signs having low-s.

Closes #159

Closes #181

Closes #135

Introduce sha3 crate and use it in ethash

Multithreaded block queue

Closes #172

Iterator for NibbleSlice and TrieDB.