Protect against empty data.
Renamed coin and currency to p1, p2 (a pair).
coe.py is gone.
Sorted changes, see the larger message.

Added a namedtuple for Ticker events (btce and mtgox are producing them
for now);

The functionality of coe.py has been moved to btcx/common.py in the
form of a Mixin. Only MtgoxFactoryClient is using it (the functionality
provided is mostly relevant when using a protocol that is not readily
available, i.e. websockets in this case);

Removed custom __getattr__ from MtgoxFactoryClient, demo_1 was adjusted
to use the new functionality provided by CallOnEvent instead;

Updated demo_4, demo_7 so they do not rely on coe module;

HTTPAPI now passes **kwargs to the callbacks;

Less print and more log.msg for MtgoxProtocol;

New methods (ticker_fetch and currency_info) for the public HTTP API in
MtgoxProtocol. Also, these methods that accepts pairs of currency now
properly support them;

Adjusted _handle_remark in MtgoxProtocol to deal with results from HTTP
API v1 and v2 at the same time. Failed calls are also handled now (in
_handle_remark);

Whew!