Pre-Publication Review of Host Spec

[FlorianFranzen]

Skipped chapters:

• C07 AnV
• C08 Messaging

Stage 1 - Spec Team

• [x] C01 Background @lamafab (#419)
• [x] C02 State @lamafab (#419)
• [x] C03 Transition @FlorianFranzen (#439)
• [x] C04 Networking @drskalman (#435)
• [x] C05 Bootstrapping @FlorianFranzen
• [x] C06 Consensus @drskalman (#435)
• [x] A Cryptoalgorithms @drskalman (#446)
• [ ] B Encodings @FlorianFranzen
• [x] C Genesis @lamafab (#419)
• [ ] D Hostapi @FlorianFranzen
• [x] E Runtimeapi @drskalman (#446)

Stage 2 - Research Team

• [ ] C01 Background @AlfonsoCev
• [ ] C02 State @AlfonsoCev
• [ ] C03 Transition @AlfonsoCev
• [x] C04 Networking @infinity0 -> #403
• [x] C06 Consensus @hndnklnc (through pdf/florian) @AlistairStewart (through Syed)

[drskalman]

• [ ] C04 network @skalman's review -> f3ee88da

[FlorianFranzen]

* [ ]  C04 network @Skalman's review -> [f3ee88d](https://github.com/w3f/polkadot-spec/commit/f3ee88da4868a9e3117f377adb409b02a8f31321)

This was included in #435. I updated the issue accordingly.

[drskalman]

Encoding is almost done. We might change the ordering based on @AlfonsoCev 's feedback.

[FlorianFranzen]

Apart from chapter 3, all chapters underwent some basic review.