correct handling of ISO 8601 timezone format
correct handling of ISO 8601 timezone format
Make String serialize empty string to empty string instead of null

This makes the following True:
``` String().serialize(node, u'') == u'' ```

Issue #72
we arent going to release a 3-dot float-fear colander
Merge branch 'master' of github.com:Pylons/colander
Merge branch 'string_type_serialize_empty_string' of git://github.com/tranminhh/colander into tranminhh-string_type_serialize_empty_string
add change note
make tests pass on 3.2
add Py33 trove classifier
prep for 1.0a1
specify
- Add ``colander.ContainsOnly`` and ``colander.url`` validators.
Add myself to CONTRIBUTORS.
Iso datetime format can be truncated.

Correct ISO8601_REGEX to support truncated time part in the
datetime representation, and add corresponding tests: now we support
time stamps truncated to the minute, the hour or the day:

    2007-01-25T12:00Z
    2007-01-25T12Z
    2007-01-25
Merge branch 'contributor_agreement' into iso8601_truncation
rename acceptable to choices
prep for 1.0a2
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'origin/master'

Conflicts:
	colander/iso8601.py
added some tests for #65 - handling of ISO 8601 timezone format