Arbitrage

[zyzek]

• Completed the arbitrageur bot so that it can participate in all six available triangular arbitrage cycles;
• Added new logic for _sell_quoted_ function;
• Gave MarketPlayer a slightly briefer means of accessing its markets;
• Agents now have a record of what trades they have made;
• Additional fee functions available to order books;
• More complete docstrings and types in various places;
• Improved ask/bid logic;
• Additional utility functionality in the orderbook (e.g. quantity functions);
• Some members renamed for clarity and sense;
• Rounding fixes;

Closes #38.
Closes #3.

[0xdomrom]

There seems to be an issue with making certain currencies unavailable. Probably stemming from updating values/fees, even though the logic seems sound. I'm looking into the issue, which probably existed beforehand, and do not want to merge until some headway is made into solving this.

[zyzek]

In principle I agree that this shouldn't be merged until those issues are dealt with, but I wonder if we could put that into a separate PR?

Happy to keep it here if they were problems introduced by this patch, but if they were pre-existing then it would be good to get these arbitrageurs and other improvements into the master version.

[0xdomrom]

I think some of the issues did come with the changes here, so for now, I'll close this.