Fix parsing of boolean parameters

Parsing of boolean parameters is not strictly conforming to xsd specification ( http://www.w3.org/TR/xmlschema-2/#boolean), which allows only values true, false, 0 and 1.

All other values should be considered as an invalid parameter.

The current implementation doesn't process "0", which is then interpreted by ruby as true.

It also doesn't raise an error if some invalid parameter is in the request.

The pull request adds specs and the fix in params.rb for this issue.