CapWords convention for class names

[oyamad]

PEP8 writes

Class names should normally use the CapWords convention.

There are a few cases that do not follow this in two_auctions and house_auction (there may be other such files):

lecture-python.myst/lectures/two_auctions.md

Line 550 in 22983b3

class bid_price_solution:

lecture-python.myst/lectures/house_auction.md

Line 672 in 22983b3

class ascending_bid_auction:

lecture-python.myst/lectures/house_auction.md

Line 1214 in 22983b3

class GC_Mechanism:

Consider changing to BidPriceSolution and so on.