pred_curve: Predict Aging Curve
In guytuori/simScores: Similarity Scores for Baseball Players

Predicts the aging curve for a sequence of ages using the fixed effect coefficients from a fitted model

1	pred_curve(ages, coefs, poly_model)

`ages`	numeric. The ages for which to estimate the player's aging curve.
`coefs`	The coefficients from the fitted model. Can be either a vector or a matrix where each column consists of a different set of coefficients.
`poly_model`	the model used to decompose the `ages` vector into orthogonal polynomials. Must have degree equal to the number of rows in the `coefs` matrix or, if `coefs` is a vector, the length of `coefs`.