This commit introduces a new file scanner-driver.c that contains the
implementation of functions related to the scanner driver.

Signed-off-by: Akarshan Kapoor <data.akarshan@icloud.com>

This commit updates Scanner.h to closely follow the Mopria Scan
specifications. We should now have a very detailed implementaion of
scanner.h that closely follows the structure of printer.h while also
following the Mopria Scan specifications.

Signed-off-by: Akarshan Kapoor <data.akarshan@icloud.com>

This commit adds some basic features to closely follow
the printer-private.h file. The updated scanner-private.h should be
the final version of this file (for now).

Signed-off-by: Akarshan Kapoor <data.akarshan@icloud.com>

- Implemented scanner-specific event handling and introduced new events for scanner operations.
- Added `scanner-escl.c` for eSCL-specific scanner state management.
- Modified `job-process.c`, `job.c`, `printer-accessors.c`, and `scanner-accessors.c` to integrate scanner event functions.
- Updated `system-subscription.c` to support scanner events and added `papplSystemAddScannerEvent`.
- Enhanced `system-private.h` and `subscription.h` with new scanner event types and callback definitions.
- Included necessary changes in `Makefile` and other system-related files for compatibility.

Signed-off-by: Akarshan Kapoor <data.akarshan@icloud.com>

This commit updates the Readme and Build files to
include libxml2 as a dependency.

Signed-off-by: Akarshan Kapoor <data.akarshan@icloud.com>

This commit finalises the scanner-driver.c file. It includes all the
functions as required for working with scanner-drivers and closely in
line with the printer-driver.c file.

Signed-off-by: Akarshan Kapoor <data.akarshan@icloud.com>

This commit finalises the scanner-webif.c file.
It closely follows all aspects of the printer-webif.c file, but
also follows the scan specific requirements.

This commit finalizes the implementation of the scanner web interface
functions, including the following features:

- Added `_papplScannerWebConfig()` to show and handle scanner configuration settings.
- Implemented `_papplScannerWebConfigFinalize()` to save changes to the scanner configuration.
- Developed `_papplScannerWebDefaults()` to display and update default scanning settings.

Signed-off-by: Akarshan Kapoor <data.akarshan@icloud.com>

This commit finalises the scanner.c file. It is closely in reference to
the printer.c file, while also covering the necessary details of
eSCL Scanning.

Signed-off-by: Akarshan Kapoor <data.akarshan@icloud.com>