connector/github: enable private, primary emails

Documentation: removed private emails caveats section

Log large bcrypt costs, error if password-hash comparison takes > 10s

connector/github: multiple orgs, query by teams

Documentation: examples of GitHub `orgs` field with multiple orgs
and org with teams; note legacy behavior

Fix documentation link

connector/oidc: fix hosted domain support.

The bcrypt hashing algorithm runtime grows exponentially with cost,
and might cause a timeout if the cost is too high. Notifying the user
of high cost and of long running calculations will help with tuning
and debugging.

Update deps

server/rotation.go: Fix key rotation with multiple dex instances.

.travis.yml: bump golang version to 1.8.3

scripts: bump builder to Go 1.8.3

Documentation: add a group query example for the ldap connector.

bugfix: avoid generating an invalid ID attribute in SAML's AuthenRequest element

Google hosted domain support

Avoid generating an identifer which starts with a number because it may be used as a SAML's ID attribute

examples: document explicit flow in example config

Update using-dex.md

Update using-dex.md

Documentation/github-connector: warn user that GitHub email id should be public.

connector: improve error message for callback URL mismatch

Documentation/ldap-connector.md: Warn about LDAP connector's bindPW restriction.