Add GAPIC docs to docs site

[jdpedrie]

This change adds the generated GAPIC clients to the Google Cloud PHP docs site. It takes advantage of GoogleCloudPlatform/gcloud-common#213, so we'll need to rebuild the docs site before this is merged.

• Add all generated clients to the table of contents.
• Add simple landing pages (README.md) in empty folders.
• Modify doc generator to recognize external types specified in docs/external-classes.json and transform references into external links.

For an example, see https://jdpedrie.github.io/gcloud-php/#/docs/master/servicebuilder.

This closes #99.

[dwsupplee]

Cool stuff! A few notes:

• We should see if we can get the clients regenerated to include params and returns in the doc blocks so that methods such as LoggingServiceV2Client::formatLogName are more descriptive. /cc @michaelbausor
• There are a handful of types which seem like they need to be added to the external classes map. For example, sslCreds in LoggingServiceV2Client::__construct and resource in LoggingServiceV2Client::writeLogEntries.

[michaelbausor]

Filed an issue to update those docs: googleapis/gapic-generator#1089

[jdpedrie]

@michaelbausor do you know of any reference documentation for Grpc\ChannelCredentials which I could link to? grpc.io has API documentation for the PHP library only, not for classes created by the extension.

[michaelbausor]

Not that I'm aware of. It is coming from here: https://github.com/grpc/grpc/blob/master/src/php/ext/grpc/call_credentials.h#L49

[dwsupplee]

Docs for classes like Grpc\ChannelCredentials would be incredibly helpful. That seems like something we should push for.

@jdpedrie Besides the aforementioned, it looks like there are other types that are not being linked out to. serviceFilter and timeRange found in ErrorStatsServiceClient::listEvents are examples of others. Scrolling through the docs I'm seeing them rather frequently. Can we do a review to make sure they're all getting hit?

[jdpedrie]

@michaelbausor one more thing...

https://github.com/GoogleCloudPlatform/google-cloud-php/blob/master/src/Monitoring/V3/MetricServiceClient.php

Lots of links in this file that will not work on the docs site.

For instance:

[filter](/monitoring/api/v3/filters)

Looks like they all just need to be prefixed with https://cloud.google.com.

[jdpedrie]

@dwsupplee updated the rest of the refs to external classes I could find (save ChannelCredentials) and regenerated the docs site on my fork.

[dwsupplee]

👊