feat: make the project installable with a Makefile

[Tachi107]

This patch adds a small POSIX Makefile so that Doxygen Awesome can be easily installed, by running make install.

The file works on Linux, BSDs, macOS, and possibly even Windows.

This is mostly useful for distributions, so that they can easily package this project in a uniform way; in fact, I wrote this because I'm packaging Doxygen Awesome for Debian :)

A default installation would look like this:

$ tree usr
usr
└── local
   └── share
      └── doxygen-awesome-css
         ├── doxygen-awesome-darkmode-toggle.js
         ├── doxygen-awesome-fragment-copy-button.js
         ├── doxygen-awesome-interactive-toc.js
         ├── doxygen-awesome-paragraph-link.js
         ├── doxygen-awesome-sidebar-only-darkmode-toggle.css
         ├── doxygen-awesome-sidebar-only.css
         └── doxygen-awesome.css

[jothepro]

in fact, I wrote this because I'm packaging Doxygen Awesome for Debian

Wow, cool to hear that! 😎

If I understand it correctly a user could use this Makefile (or the debian package) to install the theme globally on the system and then reference it with absolute paths from a project documentation? Or one could also override the PREFIX variable and use the makefile for a local install into a project directory?

It would be nice if you could provide some documentation of the feature and how it can be useful, either in the README or maybe on "Tips & Tricks"? Otherwise I can also try to put it in my own words and ask for your feedback. 😊

[Tachi107]

Yep, exactly! I'll add some documentation as soon as possible :)

[Tachi107]

I've added a couple of lines to the readme, let me know if I need to tweak something :)

I could've added that you'll be able to also install the theme on Debian and Ubuntu with apt install doxygen-awsome-css, but the package hasn't been accepted yet

[jothepro]

Perfect, thx! I'm looking forward to your PR once the package is available!