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
Allow dots in property names.

This is for vCard compatibility. From RFC 6350:

    The group construct is used to group related properties together.
    The group name is a syntactic convention used to indicate that all
    property names prefaced with the same group name SHOULD be grouped
    together when displayed by an application.  It has no other
    significance.  Implementations that do not understand or support
    grouping MAY simply strip off any text before a "." to the left of
    the type name and present the types and values as normal.

We could of course consider stripping off the group prefixes, but then
that data would be lost. I recommend we leave this to the user or
Component subclasses to do something meaningful with groups.
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
Merge remote-tracking branch 'untitaker/vcard_groups'
allow dots in property names
prepare release
back to dev
Revert API breakage
Add CHANGES entry for parent commit
prepare release
back to dev