This is a new Similarity implimention for the contrib/miscellaneous/ package, it provides a Similiarty designed for people who know the "sweetspot" of their data. three major pieces of functionality are included:
1) a lengthNorm which creates a "platuea" of values.
2) a baseline tf that provides a fixed value for tf's up to a minimum, at which point it becomes a sqrt curve (this is used by the tf(int) function.
3) a hyperbolic tf function which is best explained by graphing the equation. this isn't used by default, but is available for subclasses to call from their own tf functions.
All constants used in all functions are configurable. In the case of lengthNorm, the constants are configurable per field, as well as allowing for defaults for unspecified fields.