Correct seperation of `ParleyNetworkSession`

[mat1th]

As discussed in https://github.com/parley-messaging/ios-library/issues/77 fixed the for the flowing issues:

• Use application/json instead of multipart/form-data (your spec of the API does not include JSON but the requests do work https://api.parley.nu/clientApi/v1.8/doc/#operation/PostMessages)
• Improve the ParleyNetworkSession interface so you do not need to serialize the data in the implementation of the interface.

[alexkok]

(your spec of the API does not include JSON but the requests do work https://api.parley.nu/clientApi/v1.8/doc/#operation/PostMessages)

Yeah correct, we've already send that as feedback to update the docs 👍

Just to verify: This also fully resolves the wanted implementation way for resolving #77 ?

Anyway, these changes look good! We will test these changes tomorrow and proceed to releasing 🚀

[mat1th]

Good to hear that the docs will be updated. Yes, this fixes the issues described in #77.

[alexkok]

Thanks! Released in 4.0.1 🚀

[mat1th]

Thank you for releasing!