A repository for binary packages contains the packages itself, and
an index file describing the information about available packages.

The structure for this file is just the same than the plist file used
to register installed packages, aka "an array of dictionaries" and
a "dictionary per package".

The package dictionary will be the same than the one available in
package's metadata directory "/var/cache/xbps/$pkgname/props.plist",
but some additional objects are added to provide enough info for
the repository itself.

Here's how the package index plist file shall look like in a repository:

<dict>
	<key>xbps_available_packages</key>
	<array>
		<dict>
			<key>pkgname</key>
			<string>klibc</string>
			<key>version</key>
			<string>1.5.17</string>
			<key>filename</key>
			<string>klibc-1.5.17.x86_64.xbps</string>
			<key>architecture</key>
			<string>x86_64</string>
			<key>installed_size</key>
			<integer>9471141</integer>
			<key>maintainer</key>
			<string>Juan RP xtraeme@gmail.com</string>
			<key>short_desc</key>
			<string>Minimal libc subset for use with initramfs</key>
			<key>long_desc</key>
			<string>
 klibc is intended to be a minimalistic libc subset for use with initramfs.
 It is deliberately written for small size, minimal entanglement, and
 portability, not speed. It is definitely a work in progress and a lot of
 things are still missing.</string>
			...
		</dict>
		...
	</array>
</dict>