Adds a dedicated Python API

[ilumsden]

This PR adds a dedicated Python API to DYAD. This API will not be built/installed by Autotools. Instead, it will use setuptools/pip for its build/install process. This will allow us to host the Python API on PyPI if desired.

In terms of the interface, there are only 3 things a user may have to interact with:

1. The dyad_open function
2. The dyad_open_local function
3. The Dyad class

Most users will only use dyad_open. This function is a drop-in replacement for the built-in open function. Internally, this function is a "context manager" (see this page for more info). It creates a global Dyad object (if not created previously) and uses the Dyad object and built-in open function to carry out data production/consumption. When using dyad_open, DYAD will always be configured with environment variables.

The dyad_open_local function is provided to allow users to programmatically configure DYAD. When using dyad_open_local, users will first manually create a Dyad object and initialize it with the init or init_env methods. Then, users will invoke dyad_open_local. This function takes the same arguments as the built-in open plus an additional positional argument called dyad_ctx. This argument is the last required positional (i.e., it comes after all positionals from the built-in open function), and it accepts a pre-initialized Dyad object.

This PR is currently work-in-progress. The API is mostly complete, but packaging (i.e., setuptools stuff) and basic testing are still required.

[JaeseungYeom]

Is this PR is off the unmerged DTL PR? The reason I am asking is it is difficult to see what changes are relevant to the purpose of the PR.

[JaeseungYeom]

Is is still work in progress PR?

[ilumsden]

All that's left is testing to make sure it works correctly. Haven't gotten to that yet.

[ilumsden]

@JaeseungYeom @hariharan-devarajan @vsoch now that the DTL PR is merged, I've fixed up this PR. It's now fully ready for review.