Return undefined from util.decode on more invalid inputs

Specifically, on inputs with components that are invalid
base64. Previously, such input would produce an exception,
which is inconsistent with the behavior for other forms
of invalid input (wrong number of components, wrong IV
length, invalid JSON).
Merge pull request #77 from mapbox/decode-invalid

Return undefined from util.decode on more invalid inputs
update docs
Merge pull request #84 from jgoldbeck/secure-proxy

Update docs for secure proxy
added `destroy` as an alias for `reset` to have compatibility with other express session store
Merge pull request #89 from lemieux/master

added `destroy` as an alias for `reset` to have compatibility with other...
Exporting the destroy() method on session objects.

This is a follow up to PR #89.
Merge pull request #91 from rdegges/master

Exporting the destroy() method on session objects.
bump cookies to 0.5.0
v0.7.0