Deprecate Plugin::HookCallFunction(), replace with HookFunctionCall()

This also changes the argument type of Func::operator() to zeek::Args*
to allow plugins to be able to alter function arguments in place as
was previously documented.

testing/btest/plugins/func-hook-plugin/src/Plugin.cc

@@ -0,0 +1,86 @@
+
+#include "Plugin.h"
+
+#include <Val.h>
+#include <Func.h>
+#include <Event.h>
+#include <Conn.h>
+#include <Desc.h>
+#include <threading/Formatter.h>
+
+namespace plugin { namespace Demo_Hooks { Plugin plugin; } }
+
+using namespace plugin::Demo_Hooks;
+
+plugin::Configuration Plugin::Configure()
+	{
+	EnableHook(HOOK_CALL_FUNCTION);
+	EnableHook(META_HOOK_PRE);
+	EnableHook(META_HOOK_POST);
+
+	plugin::Configuration config;
+	config.name = "Demo::Hooks";
+	config.description = "Exercises all plugin hooks";
+	config.version.major = 1;
+	config.version.minor = 0;
+	config.version.patch = 0;
+	return config;
+	}
+
+static void describe_hook_args(const plugin::HookArgumentList& args, ODesc* d)
+	{
+	bool first = true;
+
+	for ( plugin::HookArgumentList::const_iterator i = args.begin(); i != args.end(); i++ )
+		{
+		if ( ! first )
+			d->Add(", ");
+
+		i->Describe(d);
+		first = false;
+		}
+	}
+
+std::pair<bool, IntrusivePtr<Val>> Plugin::HookFunctionCall(const Func* func,
+                                                            Frame* frame,
+                                                            zeek::Args* args)
+	{
+	ODesc d;
+	d.SetShort();
+	HookArgument(func).Describe(&d);
+	HookArgument(args).Describe(&d);
+	fprintf(stderr, "%.6f %-15s %s\n", network_time, "| HookFunctionCall",
+		d.Description());
+
+	if ( streq(func->Name(), "foo") )
+		{
+		auto& vl = *args;
+		vl[0] = val_mgr->Count(42);
+		}
+
+	return {};
+	}
+
+void Plugin::MetaHookPre(HookType hook, const HookArgumentList& args)
+	{
+	ODesc d;
+	d.SetShort();
+	describe_hook_args(args, &d);
+	fprintf(stderr, "%.6f %-15s %s(%s)\n", network_time, "  MetaHookPre",
+		hook_name(hook), d.Description());
+	}
+
+void Plugin::MetaHookPost(HookType hook, const HookArgumentList& args, HookArgument result)
+	{
+	ODesc d1;
+	d1.SetShort();
+	describe_hook_args(args, &d1);
+
+	ODesc d2;
+	d2.SetShort();
+	result.Describe(&d2);
+
+	fprintf(stderr, "%.6f %-15s %s(%s) -> %s\n", network_time, "  MetaHookPost",
+		hook_name(hook), d1.Description(),
+		d2.Description());
+	}