Add meta data to test type convertion for dates, times and rationals.
Modify GPS meta data to test "real" rationals.
Add specs to test typed return falues.

Time object tests use IPTC release date/time. Exif GPS data
is used for testing multiple rationals.
Existing test are using fixnums instead of strings now.

Rational helper is required because Ruby 1.8 and 1.9 are using
different methods to create rationals.
Add methods to convert exiv2 values to ruby objects based on there type.
Fix test for string encoding in each.
Merge branch 'types' of github.com:jgraichen/exiv2 into types
Add write support for multiple values and multiple properties.

Also:
* Change return value for xmp langAlt values.
* Check for exif repeatable properties.