The draft by the late Reinhold Bader (1966-2024) about OOP features
in Fortran is added to the learning section.  Except the addition to
the `learning.yml` file and a boiler plate header in the mandatory
`index.md` file, it is a copy-paste of the illustrations and the
text provided by `pandoc_md.md`, commit a77670d by 2024-09-03 of
the rescuing GitHub repository.[1]

[1] https://github.com/nbehrnd/bader_article

Signed-off-by: Norwid Behrnd <[email protected]>

Signed-off-by: Norwid Behrnd <[email protected]>

The contribution page[1] describes optional admonition environments
which could help to retrieve hints.  It is tested on one case.

[1] https://fortran-lang.org/en/community/contributing/

Signed-off-by: Norwid Behrnd <[email protected]>

Now each instance of string `_Hint:_` is substituted by an
admonition environment.

Signed-off-by: Norwid Behrnd <[email protected]>

Snippets of code in the learning section indent with 2 spaces per
level eachl.  This pattern now is used, mostly with help of findent.

Signed-off-by: Norwid Behrnd <[email protected]>

Following the requested Code style,[1] snippets of code which show
a principe but as such can not be successfully compiled no longer
carry the `f90` label.  The presence of at least one colon `:`,
or one elipsis `...` is considered as an indicator.

[1] https://fortran-lang.org/en/community/contributing/

Signed-off-by: Norwid Behrnd <[email protected]>

The usage of the two illustrations were edited; they now are block
level images.[1]

[1] https://myst-parser.readthedocs.io/en/latest/syntax/images_and_figures.html

Signed-off-by: Norwid Behrnd <[email protected]>

Following a recommendation,[1] keywords of Fortran in the snippets
of code, running text, and section headers now are set in lower-
case characters only.  Beside syntax highlighlighting the web site
offers, this then is more consistent in style with the other booklets
already present.  There however are exceptions to this change in the
table about value statements, section Performing I/O with objects of
container-like type).

[1] fortran-lang#477

Signed-off-by: Norwid Behrnd <[email protected]>

Bader's draft about the support of OOP by Fortran now equally is
accessible from the centre (section Fortran documentation) as well
as from the lateral menu of the booklets.  The entry in the later
is new by this commit.

Signed-off-by: Norwid Behrnd <[email protected]>

The booklet's content now is organized in three pages.  This deviates
from the state of commit a77670d (2024-09-03) of the rescuing GitHub
respository,[1] however likely reflects better the original intent by
Bader.

[1] https://github.com/nbehrnd/bader_article

Signed-off-by: Norwid Behrnd <[email protected]>

A light edit to improve the aesthetics of the eventual rendering
as html file.  The cross-links within the booklet are removed because
I don't understand the working of internal site links as explained by
the guidelines,[1] nor successfully identified a working example among
the other booklets by others.

[1] https://fortran-lang.org/en/community/contributing/

Signed-off-by: Norwid Behrnd <[email protected]>