Re-purposed @wbic32

@wbic32 now gives Bitcoin trading advice on a daily basis. The algorithm
is a crude average mechanism that compares yesterday's 'average' to
today's by assuming that yesterday's average was uniformly distributed
over the previous 29 days.

This has some important properties for trading:
0. We don't need to store much state.
1. We always under-estimate the average when the price is rising.
2. We always over-estimate the average when the price is falling.
3. We issue a buy rating when the price is 25% or more below the crude
average.
4. We issue a sell rating when the average stops changing.
5. We issue a hold rating otherwise.