specialize evalbase based on type of breaks array

[sglyon]

Right now our evalbase method for SplineParams and LinParams doesn't utilize the information in the type parameter (which specifies the type of the breaks <: AbstractVector)

Cases where breaks::Range could be sped up significantly in at least two places:

1. computing the indices specifying the lower boundary on the breaks. This could be simplified into rescaling the input point to live on 1:length(breaks) and then adjusting the endpoints
2. Computing the actual basis matrix: here we wouldn't need to do lookups of adjacent points in breaks and dividing by their difference -- that difference is the same constant for all pairs of adjacent breaks.