create a weightings syntax for normal generation

[eviltester]

Create a weightings construct used in Generation - not combinations

e.g.

specific values get increased probability of occuring

[field name].weightings({"",0.2},{"Bob",0.2})

specific ranges get increased probabilyt of occuring

[field name].weightings({<16,0.5},{>16 AND < 32, 0.3})

When given weightings values do not == 1 then other values are given the remaining probability range

If given weightings ==1 then this is not an error, it just means the user has decided to only use the values or ranges in the weigtings.