Be less strict about bad percent encoding

1.3.12 (2013-12-28):

• Be lenient about decoding incorrect encoded percent-strings (mirage#31).
• Improve ocamldoc for Uri.of_string.
• Regenerate build files with OASIS 0.4.1.
• Add an mldylib to build the cmxs Natdynlink plugin properly (mirage#29).