Allow XML::Reader to be used without specifying a backend - defaults to XML::Reader #1
This pull request is motivated by this year's CPAN Pull Request Challenge.
The change allows to 'use XML::Reader;' without specifying a backend. In that case, XML::Reader will now try to load XML::Parser, and if this fails, fall back to XML::Parsepp. This is similar to the behaviour of the modules Text::CSV or JSON which also have a XS and a pure perl implementation.
Tests simulating the absence of modules are included in the xt/author section, so that they will not be executed during an install.
Documentation is amended in English and German - but I fail to speak French, so I have to apologize that the French version is missing.