When developing agent modules or binary tools which use Zabbix headers, the headers need to be manually downloaded, extracted and added to the include paths. This can cause complexity for Makefiles and packaging tools.

It would be handy to have a `zabbix-devel` package to install the headers into `/usr/include`, ready for developers to make easier use of.

Ideally, these might be addressable by version also, as there are broken compatibilities in the headers between v2 and v3 (see: ZBX-10428).