gtoolbar: A toolbar constructor
In jverzani/gWidgets2: Rewrite of gWidgets API for Simplified GUI Construction

A toolbar can be added to a main window to proxy various actions. Toolbars can also contain various widgets, such as buttons, checkboxes, radio buttons, etc. These should be constructed using a parent argument – not a container argument. In gWidgets2 a toolbar is specified by a list of toolbar items. The svalue and svalue<- methods may be used to get or set the items.

generic for toolkit dispatch

A toolbar item is a list of action items or a toolbar instance

for a toolbar, svalue<- replaces the toolbar items with new ones specified by value.

gtoolbar(toolbar.list = list(), style = c("both", "icons", "text",
  "both-horiz"), container = NULL, ..., toolkit = guiToolkit())

.gtoolbar(toolkit, toolbar.list = list(), style = c("both", "icons", "text",
  "both-horiz"), container = NULL, ...)

## S3 method for class 'GToolBar'
add(obj, child, expand = FALSE, fill = NULL,
  anchor = NULL, ...)

## S3 replacement method for class 'GToolBar'
 svalue(obj, index=NULL, ...) <- value

`toolbar.list`	list. A one-level list of `gaction` items, `gseparator` items or possibly other widgets. In the latter cases the `container` argument is not specified prior. (XXX Need to work this out with gWidgetstcltk)
`style`	style for icon or text.
`container`	a GWindow instance
`...`	ignored
`toolkit`	toolkit
`obj`	parent object
`child`	child widget
`expand`	NULL or logical. For box containers controls whether a child will expand to fill the allocated space.
`fill`	NULL or character. For box containers. The value of `fill` (not always respected) is used to control if expansion happens vertically (`y`), horizontally (`x`) or both (`both` or `TRUE`). For vertically filled box containers, children always fill horizontally (atleast) and for horizontally filled box containers, children always fill vertically (atleast). This is important to realize when trying to size buttons, say.
`anchor`	NULL or integer. For box containers. The anchor argument is used to position the child within the parent when there is more space allocated than the child requests. This is specified with a Cartesian pair in -1,0,1 x -1, 0, 1.
`index`	NULL or logical. If `TRUE` and widget supports it an index, instead of a value will be returned.
`value`	value to assign for selection or property