Revert "Rename the Python SDK library from rerun_sdk to just rerun."

[emilk]

Reverts #30

Unfortunately this caused a name-clash where two Cargo targets share the same name:

> cargo doc --document-private-items --no-deps --all-features
warning: output filename collision.
The bin target `rerun` in package `rerun v0.1.0 (/Users/emilk/code/rerun/rerun/crates/rerun)` has the same output filename as the lib target `rerun` in package `re_sdk_python v0.1.0 (/Users/emilk/code/rerun/rerun/crates/re_sdk_python)`.
Colliding filename is: /Users/emilk/code/rerun/rerun/target/doc/rerun/index.html
The targets should have unique names.
This is a known bug where multiple crates with the same name use
the same path; see <https://github.com/rust-lang/cargo/issues/6313>.

Which sometimes leads to error: failed to remove file /Users/emilk/code/rerun/rerun/target/doc/rerun/index.html`.

More info: rust-lang/cargo#6313

Hopefully we can work around this somehow. We could use a custom build directory, but that would lead to rebuilding the shared libraries twice, which isn't ideal. We could also just rename one of the targets after they have been built, which is a bit hacky but should work. In any case I don't feel it is the best use of my time to work on this right now, so for now the python library will have to remain as rerun_sdk.