Run the rml2pdf script in the rml file folder.

This allows you to use relative image path based 
on the folder which the rml file is located.

src/z3c/rml/rml2pdfscript.py

@@ -93,6 +93,11 @@ def goSubProcess(xmlInputName, outputFileName, testing=False):
         program.append('testing=1')
     program = " ".join(program)
 
+    # run the subprocess in the rml input file folder, this will make it easy 
+    # to include images. If this doesn't fit, feel free to add a additional 
+    # home argument, and let this be the default, ri
+    os.chdir(os.path.dirname(xmlInputName))
+
     # start processing in a sub process, raise exception or return None
     try:
         p = subprocess.Popen(program, env=env, stdin=subprocess.PIPE,