Use correct repr() for caselessdict

Otherwise repr() may show wrong contents, which is confusing
Typo: s/unsescape_string/unescape_string/
Properly handle multivalued parameters

This is needed for VCard 3.0
Add test for multivalued parameters
add myself to credists.rst
update issue number
merge #142
one more changelog for pull-request by t-8ch
Change class representation for CaselessDict objects to always include the class name or the class' name attribute, if available. Also show subcomponents for Component objects.
remove left-over import
simplify nested test structure, comment for running specific tox env