Necessary hard fork to further secure the network

Unfortunately as recent events have proven GameCoin has been very
vulnerable to selective mining pushing the difficulty up extremely fast.
Whilst the previous hard fork does help to alleviate some of this by
looking further into the block history when reassessing the difficulty,
it in itself is not sufficient.

This hard fork set to come into affect from block 62,550 will:

Reduce the block generation time from 2.5 minutes to 1 minute.
Reduce the block subsidy to 400 GME in line with the new block
generation time.
Change the retarget interval from every 48 blocks to every 2 blocks.
Change the max increase/decrease to the difficulty from 400% to 110%.

Due to the change in the block time and resultant change to the coins
per block this will naturally result in bringing the overall coin cap
down from 1.67 Billion to 704 million coins over the lifetime of the
coin. Subsidy halving will occur at approximately 1.6 year intervals
instead of the 4 years intended by the original specifications.
Best not to block older versions just yet.
Merge pull request #6 from Petr1fied/master

Further hard fork to increase network security.