Hostess infinite implementation

[MalditoBarbudo]

Related to issue: #65

I have a working version with infinite capability for Hostess.
I had to create a $close() method similiar to the waitress one, to be able to send an end signal to the ldBar element, as in the original code the bar was only closed when reaching 100%.
This means that when using the infinite switch, the Hostess object must be closed when the calculations end:

### waiter + hostess normal
library(shiny)
library(waiter)

ui <- fluidPage(
  use_waiter(),
  use_hostess(),
  waiter_show_on_load(
    color = "#f7fff7",
    hostess_loader(
      "loader", 
      preset = "circle", 
      text_color = "black",
      class = "label-center",
      center_page = TRUE
    )
  )
)

server <- function(input, output){
  hostess <- Hostess$new("loader", infinite = TRUE)
  
  # for(i in 1:10){
  #   Sys.sleep(runif(1) / 2)
  #   hostess$set(i * 10)
  # }
  hostess$start()
  Sys.sleep(5)
  hostess$close()
  waiter_hide()
}

shinyApp(ui, server)

I have also updated the documentation in docs/hostess.md to add some examples using infinite, and ran all the hostess examples in the docs to check they are still working with the new changes. All seems ok, but maybe something is missed, let me know if it is ok.

[JohnCoene]

@MalditoBarbudo amazingly done!

I like the setting the bar to 95 since there is not close, works like a charm!

[MalditoBarbudo]

@JohnCoene Thanks! I thought it was a nice touch for short/medium computations, that way the bar doesn't end so abruptly :)