Allow overview pages

[zkamvar]

This will allow workshop overview pages to be processed even if they do not have any episodes.
There is a new $overview field for the Lesson object that is set to TRUE if we detect that the lesson is an overview.

For lessons built with The Workbench, this requires the overview: true YAML item. For lessons built with Jekyll, this inelegantly checks that the folder name ends with -workshop (which is violated by the LibraryCarpentry lesson using -overview, but it's moot since that lesson has episodes).

This addresses part of carpentries/workbench#65

To review this PR, start by reviewing the changes in the Lesson.R file (note: the Lesson$new() is defined by the initialize method. This is where everything flows from, which looks like this where new functions are labelled as [NEW]:

flowchart TB
   L["Lesson$new()"]
   jeky["read_jekyll_episodes()"]
   sand["read_sandpaper_lesson() [NEW]"]
   mark["read_markdown_files()"]
   sort["sort_files_by_cfg() [NEW]"]
   L -->|"jekyll=TRUE"| jeky
   L -->|"jekyll=FALSE"| sand
   jeky --> mark
   sand --> mark
   mark --> sort

Loading

I've split out the processing for the sandpaper lessons into its own function because the initializer was a little too complex.

I've also split out the functionality to sort files by the order of the config in read_markdown_files because it was also pretty complext to read initially.

NOTE: I am bumping the minor version number since this is a new feature.

Testing

You can test this version of {pegboard} by using the pull request helpers from the {usethis} package inside your local clone of {pegboard}

library("usethis")
library("devtools")
pr_fetch(132)
load_all()
# get_lesson() will download a lesson to a temporary directory and then read it in with `Lesson$new()`.
get_lesson("datacarpentry/genomics-workshop")  

When you are finished, run:

pr_finish()

If everything works, you should see this output:

<Lesson>
  Public:
    blocks: function (type = NULL, level = 0, path = FALSE) 
    built: NULL
    challenges: function (path = FALSE, graph = FALSE, recurse = TRUE) 
    clone: function (deep = FALSE) 
    episodes: NULL
    extra: NULL
    files: active binding
    get: function (element = NULL, collection = "episodes") 
    handout: function (path = NULL, solution = FALSE) 
    initialize: function (path = ".", rmd = FALSE, jekyll = TRUE, ...) 
    isolate_blocks: function () 
    load_built: function () 
    n_problems: active binding
    overview: TRUE
    path: /tmp/RtmpetwTRo/datacarpentry--genomics-workshop
    reset: function () 
    rmd: FALSE
    sandpaper: FALSE
    show_problems: active binding
    solutions: function (path = FALSE) 
    summary: function (collection = "episodes") 
    thin: function (verbose = TRUE) 
    validate_divs: function () 
    validate_headings: function (verbose = TRUE) 
    validate_links: function () 
  Private:
    deep_clone: function (name, value) 

^{Created on 2023-08-08 with reprex v2.0.2}

This will fix #118

[klbarnes20]

I have tested this and everything seems to work. I have added a few minor non-blocking suggestions.

[zkamvar]

Since Kelly gave it a positive review and the changes were nonblocking I will merge this.

Thank you for your review @klbarnes20!