This improves the API for query fns that take a sequence of generic arguments, as any type can be converted into a `RawExpr`.

Instead of returning deserialized data, this method returns reqwest::Response, giving the user more control.

This fixes the compiler complaining about the arguments not living long enough or escaping the function.
Now the query functions can take external arguments and compose well together.

Fixes #28

fixes #15

This removes the need for the user to import types from the `prometheus-http-query` crate where type annotations are required.
These changes also ensure that the public API of mquery remains more stable, as it is decoupled from the external types.