Move most code into crates/ subfolder

Cargo.toml

crates/api/Cargo.toml

crates/api/src/claims.rs

crates/api/src/comment.rs

crates/api/src/community.rs

crates/api/src/lib.rs

crates/api/src/post.rs

crates/api/src/site.rs

crates/api/src/user.rs

crates/api/src/version.rs

crates/api/src/websocket.rs

crates/apub/Cargo.toml

crates/apub/src/activities/mod.rs

crates/apub/src/activities/receive/comment.rs

crates/apub/src/activities/receive/comment_undo.rs

crates/apub/src/activities/receive/community.rs

crates/apub/src/activities/receive/mod.rs

crates/apub/src/activities/receive/post.rs

crates/apub/src/activities/receive/post_undo.rs

crates/apub/src/activities/receive/private_message.rs