Integrate client library API references

[JakeSCahill]

We should have the API references on the doc site like we've done for the IRI API.

[jakubcech]

This requires two three things essentially:

1. Plugging in the JS, Go, and Java repos into the BuildKite pipeline.
2. Making some adjustments to how the MD files are generated by the JS, Go, and Java repos. As the markdown template evolved.
3. Changing links from GitHub to the files in the docs repo file structure and adding the relevant one sin the ToC.

I'll take care of coordinating 1 and 2 once the first version of the account module is out. Until then we just link into the GitHub repo for reference files like we did.