Add gzip log writing to the ascii writer.

This feature can be enabled globally for all logs by setting
LogAscii::gzip_level to a value greater than 0.

This feature can be enabled on a per-log basis by setting gzip-level in
$confic to a value greater than 0.

testing/btest/scripts/base/frameworks/logging/ascii-gz.bro

@@ -0,0 +1,75 @@
+#
+# @TEST-EXEC: bro -b %INPUT
+# @TEST-EXEC: gunzip ssh.log.gz
+# @TEST-EXEC: btest-diff ssh.log
+# @TEST-EXEC: btest-diff ssh-uncompressed.log
+#
+# Testing all possible types.
+
+redef LogAscii::gzip_level = 9;
+
+module SSH;
+
+export {
+	redef enum Log::ID += { LOG };
+
+	type Log: record {
+		b: bool;
+		i: int;
+		e: Log::ID;
+		c: count;
+		p: port;
+		sn: subnet;
+		a: addr;
+		d: double;
+		t: time;
+		iv: interval;
+		s: string;
+		sc: set[count];
+		ss: set[string];
+		se: set[string];
+		vc: vector of count;
+		ve: vector of string;
+		f: function(i: count) : string;
+	} &log;
+}
+
+function foo(i : count) : string
+	{
+	if ( i > 0 )
+		return "Foo";
+	else
+		return "Bar";
+	}
+
+event bro_init()
+{
+	Log::create_stream(SSH::LOG, [$columns=Log]);
+	local filter = Log::Filter($name="ssh-uncompressed", $path="ssh-uncompressed",
+	                           $config = table(["gzip_level"] = "0"));
+	Log::add_filter(SSH::LOG, filter);
+
+	local empty_set: set[string];
+	local empty_vector: vector of string;
+
+	Log::write(SSH::LOG, [
+		$b=T,
+		$i=-42,
+		$e=SSH::LOG,
+		$c=21,
+		$p=123/tcp,
+		$sn=10.0.0.1/24,
+		$a=1.2.3.4,
+		$d=3.14,
+		$t=(strptime("%Y-%m-%dT%H:%M:%SZ", "2008-07-09T16:13:30Z") + 0.543210 secs),
+		$iv=100secs,
+		$s="hurz",
+		$sc=set(1,2,3,4),
+		$ss=set("AA", "BB", "CC"),
+		$se=empty_set,
+		$vc=vector(10, 20, 30),
+		$ve=empty_vector,
+		$f=foo
+		]);
+}
+