start moving templates

[maelle]

• Move current templates to a folder called BS3.
• Modified the code so that templates can be found there.
• Added a copy of BS3 templates in a folder called BS4, for having a better diff when these become actual BS4 templates.

[hadley]

A few initial comments. This would also be easier to review without the new BS4 starter templates, so I'd suggest removing for now.

[hadley]

WS

[hadley]

And in function calls below

[hadley]

Can you please follow https://style.tidyverse.org/error-messages.html ?

I think pkgdown uses rlang already, so please use abort() and then the error message should be a "must" statement, like "Boostrap version must be 3 or 4".

[hadley]

I'd make this an else statement so the overall structure is like:

if (has_parameter) {
  if (parameter_ok) {

  } else {
   abort(....)
 } else {
  3
}

Then it's more clear that the else clause if is very simple, so I think it's clearer to flip the order so that the simplest case becomes an early exit:

if (is.null(template$bootstrap)) {
  return(3)
}

[maelle]

Opened #1485 instead (but used the comments from here).