Complete the `BasicClient` examples

Some of the methods of the [`BasicClient`](https://docs.rs/parsec-client/*/parsec_client/core/basic_client/struct.BasicClient.html) do not have proper examples or not examples at all.
The examples should follow [this guideline](https://rust-lang.github.io/api-guidelines/documentation.html#all-items-have-a-rustdoc-example-c-example).