Add WASM Support

[jonaspleyer]

This PR makes the crates_io_api package able to be used in a WASM context. Some functionality such as std::time needed to be replaced with the web_time crate which exports std::time for non-wasm systems (such as x86). In total this PR does 3 things:

1. Refactor Code; exlude shared functionality in utils.rs
2. Loosen and Update Dependencies
3. Rewrite async_client.rs file such that it can be compiled with the wasm32-unknown-unknown target triple.

All tests are still passing. Users which have used this package should not be affected by any of the changes made. Let me know what you think.

[jonaspleyer]

Note that the most recent commits are part of an effort to have an intermediate package which can be used for publishing to crates.io.