Add support for dumping XMLs to the standard output.

Lib/fontTools/misc/xmlWriter.py

@@ -11,6 +11,8 @@ INDENT = "  "
 class XMLWriter(object):
 	
 	def __init__(self, fileOrPath, indentwhite=INDENT, idlefunc=None):
+		if fileOrPath == '-':
+			fileOrPath = sys.stdout
 		if not hasattr(fileOrPath, "write"):
 			try:
 				# Python3 has encoding support.

Lib/fontTools/ttx.py

@@ -15,7 +15,8 @@ usage: ttx [options] inputfile1 [... inputfileN]
     -h Help: print this message
     -d <outputfolder> Specify a directory where the output files are
        to be created.
-    -o <outputfile> Specify a file to write the output to.
+    -o <outputfile> Specify a file to write the output to. A special
+       value of of - would use the standard output.
     -v Verbose: more messages will be written to stdout about what
        is being done.
     -q Quiet: No messages will be written to stdout about what