Merge pricer and pricer-impl

[jodastephen]

Separating the API from the Implementation for pricers is a good idea, but struggles to work in practical terms. The interfaces in pricer are fine, except that they are never likely to have an alternate implementation. Fast pricers will be totally different. And alternate models tend to need to take in different parameters.

Delete strata-pricer-impl and merge all code into strata-pricer.