[2.x] DataCollections improvements

[caendesilva]

Overview

Changes needed to improve the data collections feature, that we save for v2 as they may be breaking

Support standalone Yaml files

We need to change the parsing so we don't need front matter blocks. (Fixed in #1733)

develop/docs/digging-deeper/collections.md

Line 137 in 4af2234

>warning Note that the Yaml file should start with `---` to be parsed correctly.

Normalize class name

It bugs me that it is DataCollections instead of DataCollection. This works fine when it's a facade, so DataCollections::get() is semantic* (so is DataCollection::get()), however, since these classes are also used as instances containing data, it makes less sense for it to be plural, because now calling DataCollections::markdown() implies (many) DataCollections due to the return. Singularizing this would also match the Illuminate Collection.

Additionally, no Laravel facades are plural, however our Includes is plural (and some others, but Includes is a sibling class to this and should match)

*DataCollections::get() is not fully semantic as it may imply it will return multiple collections.

[caendesilva]

We may also want to consider excluding README.md files from Markdown collections

Edit: No, this is too specific. Better for user to chain ->reject or use conditional continues

[caendesilva]

Should we add a warning if a data collection file is empty?

Edit: This now causes an exception

[caendesilva]

Fixed in #1732