storage: fix credentials issue.

Previously, if a user wanted to generate a signed URL, there was
no guarantee a credentials object would have already been
generated. By itself, generating a signed URL doesn't require a
network connection, thus the uncertainty that we would have
already fetched a token. This change requires a valid credentials
object to exist before returning the `credentials` object.
datastore: refactor privatizing of Key values.
datastore: update regression tests.
0.5.0
Fix wording.
Merge pull request #185 from marcgel/master

docs: Fix wording.
Fix spelling of "delimeter".
Merge pull request #186 from marcgel/master

docs: Fix spelling of "delimeter".
storage: use passthrough stream for buffers.
Nit. They are words (adverbs), but they don't work so well here.
Relative doc links
site: support permalinks. fixes #184
Update README.md
Make titles stand out better in API docs.
readme: Add easy links to homepage + docs

Discussed in #192

Also, Quickstart -> Quick Start
Merge pull request #189 from stephenplusplus/bufferstream

storage: use passthrough stream for buffers.
Merge pull request #190 from stephenplusplus/private-key

datastore: refactor privatizing of Key values.
Merge pull request #188 from stephenplusplus/permalink

site: support permalinks. fixes #184
Merge pull request #164 from stephenplusplus/connection

storage: fix credentials issue.