Tasks:

• Update description of BlockSync p2p messages in spec #544
• Revisit the following files
  • See if Revisit all apps/examples and decide how to _demonstrate_ ABCI++ tendermint/tendermint#7660 is still relevant
  • getting-started.md [small, 0.5 days]
  • indexing-transactions.md [small, 0.5 days]
  • abci-cli.md (review only) [small, 0.5 days]
  • what-is-tendermint.md (ABCI section) [small, 0.5 days]
  • go-built-in.md and go.md (same changes) [medium, 2 days]

Stretch goal:

• docs: add an ABCI 2.0 tutorial  #2853

DoD:

• The doc is updated, and proof-read
• No references of BeginBlock, DeliverTx, EndBlock can be found (except if the text is explicitly referring to them as obsolete)
• (Strech) The new tutorial is complete and included in doc

Original issue: tendermint/tendermint#9918