Sometimes it is interesting to know, whether to Attr are referring to
the same attribute. Note that it is not intended to provide a method for
the values, as that would be meaningless on its own and if it is used in
a more complex tasks, this is still possible with the current set of
methods, which is prefered as the complex task can then be implemented
on the outside completely.

A method to compare two Attr's for exact equality was added both to
internal and external methods.

When used with care, it is possible to bypass many strdup calls.

When used with care, it is possible to bypass many strdup calls.
To also save the instructions for the call, which are a lot of overhead
now, link time optimization is turned on. (-flto)

Sometimes a copy is useful.

As usual it should be also possible to bypass calls to strdup, while
also taking care.

The structure SH_Attr implements an HTML Attribute.