Number of threads is undocumented

How about we add these two get and set functions (as well)??

#' omx_set_cores
#'
#' set the number of cores (threads) used by OpenMx
#'
#' @param cores number of cores to use (defaults to max - 1 to preserve UI responsiveness)
#' @param model an (optional) model to set. If left NULL, the global option is updated.
#' @return - NULL
#' @export
#' @family omx misc functions
#' @references -\url{http://openmx.psyc.virginia.edu}
#' @examples
#' library(OpenMx)
#' manifests = c("mpg", "disp", "gear")
#' m1 <- mxModel("ind", type = "RAM",
#' manifestVars = manifests,
#' mxPath(from = manifests, arrows = 2),
#' mxPath(from = "one", to = manifests),
#' mxData(mtcars[, manifests], type = "raw")
#' )
#' oldCores = omx_get_cores() # get global value
#' omx_set_cores(model = m1) # set to default (max - 1)
#' omx_get_cores() # show new value
#' omx_set_cores(omxDetectCores()) # set to default (max - 1)
#' omx_get_cores() # show new value
#' omx_set_cores(oldCores) $ reset to old value
omx_set_cores <- function(cores = omxDetectCores() - 1, model = NULL) {
mxOption(model, "Number of Threads", cores)
}

#' omx_get_cores
#'
#' get the number of cores (threads) used by OpenMx
#'
#' @param model an (optional) model to get from. If left NULL, the global option is returned
#' @return - number of cores
#' @export
#' @family omx misc functions
#' @references - \url{http://openmx.psyc.virginia.edu}
#' @examples
#' library(OpenMx)
#' manifests = c("mpg", "disp", "gear")
#' m1 <- mxModel("ind", type = "RAM",
#' manifestVars = manifests,
#' mxPath(from = manifests, arrows = 2),
#' mxPath(from = "one", to = manifests),
#' mxData(mtcars[, manifests], type = "raw")
#' )
#' oldCores = omx_get_cores() # get current default value
#' omx_set_cores(model = m1) # set to default (max - 1)
#' omx_get_cores(model = m1) # show new value
#' omx_set_cores(omxDetectCores()) # set to default (max - 1)
#' omx_get_cores() # show new value
#' omx_set_cores(oldCores) $ reset to old value
omx_get_cores <- function(cores = omxDetectCores() - 1, model = NULL) {
mxOption(model, "Number of Threads")
}