New LWMA difficulty algorithm

Another hard fork that implemented LWMA or Linearly Weighted Moving Average difficulty algorithm for further improvements of difficulty adjustment according to miners hashing power. It is a work done by Zawy, same as the previous algorithm used, but with another logic of difficulty adjustment behind it. Some further improvements are to be done in order to function as intended but overall a big progress was made in this field. This was a mandatory update for which a new version was released. The hard fork took place at block 350000. So far we are satisfied with the reaction of the network to attackers with huge hash power.