allow `typ` as a keyword arg to SchemaNode

fixes #90
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Merge pull request #125 from claytron/contrib

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cleanup incongruities in docs
typo, see github issue #119
add `message` back to `Function` and emit warning

fixes #64
Merge pull request #127 from claytron/message_deprecation

add `message` back to `Function` and emit warning
a timezone of Z means UTC

Adaptation of patch presented here:
http://code.google.com/p/pyiso8601/issues/detail?id=15
default_timezone was completely untested
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Merge pull request #126 from adroullier/master

typo, see github issue #119