cmd/stvanity: New utility to create vanity device IDs
cmd/stvanity: New utility to create vanity device IDs

A potential practical use is to encode a short version of the hostname
at the beginning of the device ID.

For example:

	jb@syno:~/s/g/s/s/c/stvanity $ stvanity abc
	Want 15 bits for prefix "ABC", about 3.3e+04 certs to test (statistically speaking)
	Found ABCFPWS-JKDIFV3-E5IUAQW-DK53WVR-HY7XWBS-56H33GR-CJQI67Q-VGXRMAW
	Saved to cert.pem, key.pem

	jb@syno:~/s/g/s/s/c/stvanity $ stvanity $(hostname)
	Want 20 bits for prefix "SYNO", about 1e+06 certs to test (statistically speaking)
	Trying 554 certs/s, tested 8307 so far in 15s, expect ~32m total time to complete
	Trying 543 certs/s, tested 16277 so far in 30s, expect ~32m total time to complete
	...

The rest is just a matter of patience.

	jb@syno:~/s/g/s/s/c/stvanity $ stvanity syncthing
	Want 50 bits for prefix "SYNCTHI-NG", about 1.1e+15 certs to test (statistically speaking)
	Trying 529 certs/s, tested 7941 so far in 15s, expect ~67443 years total time to complete
	...

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/2986

plouj/syncthing,AudriusButkevicius/syncthing,TheBigBear/syncthing,toddleish/syncthing,kamadak/syncthing,imsodin/syncthing,ProactiveServices/syncthing,norgeous/syncthing,uok/syncthing,imsodin/syncthing,brgmnn/syncthing,TheBigBear/syncthing,AudriusButkevicius/syncthing,Kudalufi/syncthing,nrm21/syncthing,letiemble/syncthing,jryans/syncthing,plouj/syncthing,Kudalufi/syncthing,ProactiveServices/syncthing,kamadak/syncthing,wweich/syncthing,uok/syncthing,toddleish/syncthing,AudriusButkevicius/syncthing,cherylquirion/syncthing,Kudalufi/syncthing,lkwg82/syncthing,rumpelsepp/syncthing,wweich/syncthing,nrm21/syncthing,xduugu/syncthing,kluppy/syncthing,toddleish/syncthing,cherylquirion/syncthing,alex2108/syncthing,ProactiveServices/syncthing,kamadak/syncthing,TheBigBear/syncthing,syncthing/syncthing,jryans/syncthing,kamadak/syncthing,syncthing/syncthing,syncthing/syncthing,letiemble/syncthing,rumpelsepp/syncthing,imsodin/syncthing,lkwg82/syncthing,lkwg82/syncthing,letiemble/syncthing,le9i0nx/syncthing,le9i0nx/syncthing,kluppy/syncthing,AudriusButkevicius/syncthing,ProactiveServices/syncthing,wweich/syncthing,TheBigBear/syncthing,syncthing/syncthing,syncthing/syncthing,plouj/syncthing,nrm21/syncthing,lkwg82/syncthing,syncthing/syncthing,le9i0nx/syncthing,alex2108/syncthing,plouj/syncthing,uok/syncthing,kluppy/syncthing,norgeous/syncthing,brgmnn/syncthing,jryans/syncthing,wweich/syncthing,imsodin/syncthing,alex2108/syncthing,nrm21/syncthing,norgeous/syncthing,cherylquirion/syncthing,rumpelsepp/syncthing,le9i0nx/syncthing,alex2108/syncthing,kluppy/syncthing,imsodin/syncthing,rumpelsepp/syncthing,jryans/syncthing,xduugu/syncthing,brgmnn/syncthing,xduugu/syncthing,norgeous/syncthing,toddleish/syncthing,uok/syncthing,letiemble/syncthing,cherylquirion/syncthing,xduugu/syncthing,brgmnn/syncthing,Kudalufi/syncthing