2020-07: Exchange external security audit completed

We received a grant from NLnet foundation to pay for an external security audit of the GNU Taler exchange cryptography, code and documentation. CodeBlau now concluded their audit. You can find the final report here. We have compiled a preliminary response detailing what changes we have already made and which changes we are still planning to make in the future. We thank CodeBlau for their work, and NLnet and the European Commission's Horizion 2020 NGI initiative for funding this work.