ISBN - Add Ludwig integration

This simple patch should do the job.

I've tested the patch in #3. After installing the Ludwig module it downloaded the required libraries, so I think that the patch works well!

In the issue fork I also made the following changes:

• I documented that the library can be installed using the Ludwig module in the README file.
• In isbn_requirements() I mentioned as well that the Ludwig module is an option for installing the library.
• I tested the module by removing the library after installation and that caused a fatal error. Therefore I added a check in IsbnToolsService for the availibility of the library - and throw a RuntimeException if it is missing.

Thanks for all the improvements.

The Ludwig guide link

Instead of:

Steps:

1. Download and install the Ludwig module.
   https://www.drupal.org/project/ludwig

2. Download and install this module.

3. Ludwig generates a listing of libraries required by those modules. The
   Packages page at admin/reports/packages provides a download link for each
   missing library along with the paths where they should be placed.

It is probably better to just give to the users an official Ludwig guide link:

Ludwig Installation and Usage →

Outdated info

3. Ludwig generates a listing of libraries required by those modules. The
Packages page at admin/reports/packages provides a download link for each
missing library along with the paths where they should be placed.

This part is outdated. Ludwig has the automatic download and unpack functionality now, so no need for manual downloading and unpacking of library archives to the specified folders as previously. Both installing and updating the libraries with Ludwig is much more convenient now.

@devad
Thanks for your review! I looked at how the Address project → documented Ludwig support in their Readme file and adjusted the Readme here accordingly. I left out information about using a dev version, as I thought that may be less relevant for the ISBN project. I doubt that there will be much changes until adding Drupal 11 support will become relevant.

I guess that the Readme file in Feeds Extensible Parsers → (an other project that I maintain) also need to be updated, as that one still contains the outdated instructions.

@devad
Created 📌 Update Ludwig instructions in Readme Fixed

I merged the code!

Automatically closed - issue fixed for 2 weeks with no activity.