Consider moving to non-project mode in Vivado

[hasheddan]

Currently, Vivado's project mode is used to orchestrate the design workflow. While there are a number of advantages this offers, it also means that only one design can be targeted. Non-project mode offers more fine-grained control over the design workflow, and also does not require use of the Vivado GUI.

Switching to non-project mode would alleviate the issues described in #6.