Match BUY/SELL polarity to map to BID/ASK

[alnoki]

Presently, market.move defines the following constants:

Constant	Value
ASK	true
BID	false
BUY	true
SELL	false

ASK and BID are intended for maker activity, e.g. place_limit_order(), while BUY and SELL are intended for taker activity, e.g. place_market_order(). Hence per this schema ASK = BUY and BID = SELL, conveying that taker buys match against maker asks, and taker sells match against the maker bids.

However, also per this schema, if a user passes ASK during a taker function call, denoting that they want to sell, they will actually trigger a buy. Similarly, if a user passes BID during a taker function call, denoting that they want to buy, they will actually trigger a sell.

Hence it is proposed that BUY and SELL be modified to assume the following:

Constant	Value
BUY	false
SELL	true

Note that incentives.move shall also be updated to reflect the constant modifications.

@mkurnikov

[BriungRi]

I did originally find BID != BUY to be confusing at first. Aligning BID == BUY should help future developers who are reading through Econia code.