Moving away from proj/proj

[magnatelee]

Having the legate directory at the top of the repository is in general a bad idea and seems to have been masking issues that would otherwise have been caught and fixed. We should move away from this directory structure. Here are a couple of options (feel free to make any suggestions):

• Moving legate under a python directory at the top
• Renaming the current src to cpp, and moving legate under the src directory. @bryevdv mentions that setuptools might special case this directory structure.

[bryevdv]

AFAICT setuptools support some automatic discovery for the case of src:

https://setuptools.pypa.io/en/latest/userguide/package_discovery.html#src-layout

But we already have outlier requirements so I am not sure automatic discovery would apply to us anyway.

Big 👍 to moving away from proj/proj in any capacity.

[manopapad]

src for C++ and python for Python sounds good to me.

[magnatelee]

Sounds good. I'll make a PR for this after two major refactoring changes (#675 and #676) get merged.

[magnatelee]

Let's do this after #457 is merged too. Otherwise, there'll be a huge number of merge conflicts with that PR.