Milestones and planning

* itstools version:
* Python version:
* Operating System:

### Description

* Define the architecture to have a module-based specification : 1 module with the model itslef (everything that can be shared between use cases: Car-following / lane Changing ...) + 1 module for network description + 1 module per use case

* Priorities:

1. [Network description] Describe the architecture of network.py and add the appropriate features to the vehicle description

2. Add the ability to manage multiple pipes instead of only one: on-ramp merge / off-ramp merge / Successive pipes / sucessive on-ramps. It includes the necessity to solve the problem of transferring from one pipe to another.

3. Solve the merging issues (junctions problems)

4. Add the lane changing ability : implement the MOBIL or whatever lane change model

### What I Did

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