Set input

This is a basic framework for setting input values. It would be used like this:

```
# ==== in server.r ====
  # Set input values based on query string
  output$setInputs <- inputSetterHandler({
    values <- list()
    query <- parseQueryString(clientData$url_search)

    if (!is.null(query$n))
      values <- c(values, n = query$n)

    values
  })

# ==== in ui.r ====
    # This goes somewhere on the page
    inputSetter("setInputs")
```


Example app at: https://gist.github.com/wch/5201731

```
devtools::install_github('shiny', 'wch', 'set-input')
runGist(5201731)
```
After it starts, set the browser's URL to: http://localhost:8100/?n=200


Notes:

* Doesn't yet work for selectInputs or tabInputs (and probably others like checkboxes). The input bindings for these will have to be modified to work with this method.