Add missing parameters for the attributes xlink:actuate and xml:space.
make svg elements use xlink namespace

This is necessary (at least) in order to be able to introduce xlink:href attributes in
<image> elements. The namespace is declared at the top of the svg element for simplicity's
sake.
Explain why we open the xlink namespace in <svg> elements
Merge pull request #55 from FlorentBecker/xlink

make svg elements use xlink namespace
Do not use url(..) syntax for xlink:href

Some browsers (at least firefox) choke on that.
xml:lang and xml:base are not FuncIRIs
Merge pull request #56 from FlorentBecker/xlink

Fix usages of IRIs in svg.
Merge pull request #53 from ocsigen/attributes_misc

Add missing parameters for the attributes xlink:actuate and xml:space.
Add a W module in Html5 and Svg.
Add W to Xml_sigs.T and use it to simplify everything.
Remove Wrapped functors.
Consistent naming scheme for signatures: only T and NoWrap.