postmom_help_reg: postmom_help_reg method
In PatrickPfeifferDSc/bite: Bayesian Inference On Treatment Effects For Panel Data

Internal. Computes help quantities for posterior moments of regression coefficients.

1	postmom_help_reg(x, y, Wx, Wy, start_x, nx, start_y, sgma, rho, lambda, D)

`x`	data
`y`	outcome
`Wx`	design matrix for selection model
`Wy`	design matrix for outcome data model
`start_x`	matrix containing indices where certain observations begin in the vector sorted by treatment and panel times
`nx`	dimension of x
`start_y`	matrix containing indices where certain outcomes begin in the vector sorted by treatment and panel times
`sgma`	variance parameter matrix
`rho`	correlation parameter matrix
`lambda`	matrix of factor loadings
`D`	initial inclusion for treatment j