Fix YAMLRemoteRefParser with empty input (palantir#94)

Do not treat empty input as an invalid remote reference, since apps may
use an empty file as an on/off switch. Also add some tests for parsing,
since there are several edge cases now.

Fix formatting error in caching_client_creator.go (palantir#93)

Upgrade google/go-github to v35 (palantir#81)

Upgrade google/go-github to v33 (palantir#63)

Apply caching middleware for token client (palantir#57)

Add error callbacks that emit metrics (palantir#53)

These are non-default because they require a metrics registry, but the
default handlers are now implemented by passing a nil registry to the
metric version.

Note that this contains an API break in the AsyncErrorCallback type, but
I don't expect there to be many (any?) custom implementations.

add ability to configure Timeout for http.Client (palantir#48)

* centralize all http.Client creation

* set the timeout from the clientCreator

* add the configuration method

* add example and readme

* lint

* Update client_creator.go

Excavator: Update godel to latest version (palantir#41)

Co-authored-by: svc-excavator-bot <[email protected]>

Convert to go mod (palantir#35)

Add InitializeResponder to improve testing (palantir#34)

Allow code other than the default dispatcher to initialize a request
context for use with Set/GetResponder.