Add r2yara cli tool

[trufae]

The idea is to have a cli tool to download and manager your yara rule database in your home, all those rules are loaded by the yara plugin. We may have a yara rules-source database somewhere, and let the user download and update new ones for the purpose they need. This tool can be written in Python or the language of choice, as it may be probably running json+rest requests on endpoints to search and download those, and in some cases this requires api keys like for virustotal.

Some rule databases around:

• https://github.com/StefanKelm/yara-rules
• https://developers.virustotal.com/reference/list-crowdsourced-yara-rules
• https://github.com/InQuest/awesome-yara
• https://malpedia.caad.fkie.fraunhofer.de

[radare]

This tool can be written in r2js, python or C, ideally it should just spawn r2 and do whatever its needed to generate the yara rules from the options given.

I would probably wait a little for more feedback and discussions to get this done.