obj_fun: Objective function from parameters
In mbr: Mass Balance Reconstruction

This is a wrapper for lsq_mb(). It first calculates hat, then calls lsq_mb(). This is used in optim(), so it returns a scalar.

1	obj_fun(beta, X, Y, lambda, mus, sigmas, log.seasons, log.ann, N, sInd)

`beta`	Parameters
`X`	Inputs, must have columns of 1 added
`Y`	Observed Dry, Wet, and Annual log-transformed flows
`lambda`	Penalty weight.
`mus`	A vector of means, one for each target.
`sigmas`	A vector of the standard deviations, one for each target.
`log.seasons`	A vector containing the indices of the seasons that are log-transformed.
`log.ann`	TRUE if the annual reconstruction is log-transformed.
`N`	The number of targets (number of seasons plus one for the annual reconstruction).
`sInd`	Indices of the seasons, i.e, 1...N-1