* Add more standard ignored files for Julia

In particular, this adds documentation build artifacts generated by Documenter.jl as well as Manifest.toml, which can appear in docs/, in test/, or at the top level.

* Clarify the intent of each ignored item

Also add a few more build artifacts from BinaryProvider/BinDeps.

`deps/deps.jl` is an autogenerated file created by `BinDeps.jl`, Julia's package for managing binary dependencies.