Package mupdf on DUB

To use this package, run the following command in your project's root directory:

MuPDF for Dlang

This repository contains Dlang bindings for MuPDF and tools to auto-generate them for arbitrary versions.

Build and install from MuPDF sources, or alternatively:
```
sudo apt install -y libmupdf-dev
```
Add the package via DUB:
```
dub add mupdf
```

Import the package, and follow the MuPDF API documentation as needed, e.g.:

import mupdf;

void main() {

auto ctx = fz_new_context(null, null, FZ_STORE_UNLIMITED);
auto doc = pdf_open_document(ctx, "path/to/file.pdf");

// ...

}

Note the following remarks:

All PDF_NAME(x) macro invocations must be replaced with PDF_NAME_x shorthands.

Current known limitations of these bindings:

To generate Dlang bindings for an arbitrary version of MuPDF:

Install DPP.
Run the script generate.sh and follow usage instructions, e.g. to generate bindings for mupdf-1.19.0 run the following command:
```
./generate.sh 1.19.0
```