dub-registry search should include sub-packages

[Element Green]

The current package search feature on https://code.dlang.org 
leaves a lot to be desired. It doesn't support sub-string 
searches, so the exact word has to match ("gtk" wont match "gtk4" 
for example). It also doesn't search dub sub-packages.

The [giD](http://gid.dub.pm/) project currently consists of 28 
library bindings which are all sub-packages. These will not be 
found using the search feature.

This seems like a fairly major barrier to people adopting the D 
language. The dub package registry is an authoritative source for 
libraries which are supported by D and I can see how it might be 
easy for a potential D programmer to shy away from the language, 
because they can't find support for a given library they want to 
use. For example, Gtk4.

I'm currently looking into improving the search feature in 
[dub-registry](https://github.com/dlang/dub-registry), but I 
wanted to see if anyone has any thoughts, tips, or if there are 
any current efforts to improve things, before I spend too much 
time on it. Any suggestions on better ways to communicate with 
dub-registry developers would also be helpful.