Adapt sharenotify to work directly with python code snippets instead of external calls
More info: https://github.com/slush0/stratum-mining-proxy/pull/47
Add two sharenotify snippets (log and shell) as examples:

mining_proxy.py (...) --sharenotify sharenotify_snippets/shell.py
 (...)
 INFO proxy share_stats.set_module # Loaded sharenotify module sharenotify_modules/shell.py
 (...)
 INFO proxy <string>.on_share # Executing sharenotify command: echo [1393953777.77] mpool.sm2 6eff/32 >> /tmp/sharestats.log
Rename some functions to follow the general rules of the stratum-mining-proxy