improve squid logging

squid.conf

logformat squid %tl %6tr %>a %Ss/%03Hs %<st %rm %ru %un %Sh/%<A %mt

```
Time related format codes:

		ts	Seconds since epoch
		tu	subsecond time (milliseconds)
		tl	Local time. Optional strftime format argument
				default %d/%b/%Y:%H:%M:%S %z
		tg	GMT time. Optional strftime format argument
				default %d/%b/%Y:%H:%M:%S %z
		tr	Response time (milliseconds)
		dt	Total time spent making DNS lookups (milliseconds)
		tS	Approximate master transaction start time in 
			<full seconds since epoch>.<fractional seconds> format.
			Currently, Squid considers the master transaction
			started when a complete HTTP request header initiating
			the transaction is received from the client. This is
			the same value that Squid uses to calculate transaction
			response time when logging %tr to access.log. Currently,
			Squid uses millisecond resolution for %tS values,
			similar to the default access.log "current time" field
			(%ts.%03tu).
```