Fix various documentation, mostly related to file analysis.

- Fix examples/references in the file analysis how-to/usage doc.

- Add Broxygen-generated docs for file analyzer plugins.

- Break FTP::Info type declaration out in to its own file to get
  rid of some circular dependencies (between s/b/p/ftp/main and
  s/b/p/ftp/utils).

scripts/base/protocols/ftp/utils.bro

@@ -1,7 +1,8 @@
 ##! Utilities specific for FTP processing.
 
-@load ./main
+@load ./info
 @load base/utils/addrs
+@load base/utils/paths
 
 module FTP;
 
@@ -44,4 +45,4 @@ function build_url_ftp(rec: Info): string
 function describe(rec: Info): string
 	{
 	return build_url_ftp(rec);
-	}
+	}