except when serializing a collection

Unless deserializing a collection

recwarn doesn't seem to be working as expected when the whole
suite is run

Fields are responsible for determining which errors are stored

resolves #60

Fix typo

Fix another typo

A more illustrative intro example; fix typos and errors, simplify
Flask example

That parameter will soon be removed

Using normal dicts rather than OrderedDicts leads to a
significant performance improvement

If ordered=False, dump returns a regular dictionary instead
of an OrderedDict, which can lead to...

lambdas have less overhead than partials, benchmarks showed
slight performance increase using la...

In Tornado, request.body is normally a string, but it can be a
concurrent.Future on streaming re...

Resolves #56

Update examples to use callable default

Resolves #52

resolves #53

And some minor docs updates

field:value pairs for which value is None are not included in
final serialized result
resolves #54

And a few minor language updates

handle_error should just reraise error

- A "tldr;"
- Contributing docs
- kudos to colander