Add API to search for packages matching a pattern

[jaraco]

What's the problem this feature will solve?

I'd like to find all packages named "svg.*". Currently, searching for svg or svg. or svg.* or svg\. or "svg." all returns 3.7k results matching "svg" in a paged HTML form and the API limits results to 100 results. So it's not possible (as far as I can tell) to search for packages only matching a particular name without manually clicking through hundreds of HTML results.

Describe the solution you'd like

I can imagine a few solutions:

• Enable (or document) more complex search patterns, or perform more sophisticated filtering after paring down the results from the index.
• Add a UI element that allows returning all results.
• Enable an API that allows for iterating over pages of results.

[di]

Thanks @jaraco! Blocked on #284.

[feenes]

I think this might solve also an issue, that I have.

I'd like to search for packages programatically and for new projects. I'm not supposed to use the almost obsolete XMLRPC library as will disappear.

The reason I'd like to search programmatically instead of searching interactively is, that I'd like to retrieve the results by relevance but get rid of all packages, that haven't been updated for a certain (e.g. within the last year)
Too often some of the top hits are dead or unmaintained packages