Personal common go code

• logf: stupid simple file logger for debugging, use with lnav /tmp/logf
• log: structured logging based on rs/zerolog
• jsondb: based on github.com/tailscale/tailscale/jsondb
• yamldb: yaml version of jsondb
• noti: noti.Send()
• throttledtransport: throttled http.Transport for http scraping client
• downloader: generic file downloader using http.Client