[Python] Let `libqasm` be the only top level module, `v3x` being a submodule of it, and removing the need of the `cqasm` module.

[rturrado]

At the moment, when creating the Python library, we create two top level modules: libqasm, and cqasm.

The cqasm module contains a single submodule: v3x.

So, at the moment, we can import libqasm, and then import cqasm.v3x, import cqasm.v3x.ast, and so on.

The libqasm module gives us access to the V3xAnalyzer class, with the following API:

• parse_file,
• parse_string,
• analyze_file, and
• analyzer_string.

Whereas the cqasm.v3x module is also available for a more fine-grained use of the library.

import cqasm.v3x.ast
import cqasm.v3x.instruction
import cqasm.v3x.primitives
import cqasm.v3x.semantic
import cqasm.v3x.types
import cqasm.v3x.values

Ideally, I would like to have a single top level module, libqasm, with v3x being a submodule of it.