Automatic snapshot pre-release monthly-2021-04

Changes since last snapshot (monthly-2021-03)

Add an INDEX to the Instance trait (#8555)
Fix account ref-counting in session (#8538)
Introduce OnSetCode type into system config trait. (#8496)
Implement fungible::* for Balances (#8454)
[pallet-staking] Refund unused weight for payout_stakers (#8458)
Make the number of nominations configurable (#8368)
Add tracing logic in pallet macro for hooks and dispatchables (#8305)
contracts: Update deduct block when a contract is excempted (#8418)
Decouple Staking and Election - Part 2.1: Unleash Multi Phase (#8113)
staking: Flexible generation of reward curve and associated tweaks (#8327)
contracts: Expose rent parameter to contracts (#8231)
pallet-staking: add RewardDestination::None for explictly not receiving rewards (#8168)
Return babe configuration information in the babe api epoch functions (#8072)
Assets: Remove zombies, introduce approvals (#8220)
Self-sufficient account ref-counting (#8221)
Init RuntimeLogger automatically for each runtime api call (#8128)

Storing multiple Justifications per block (#7640)
Remove legacy network protocol (#8296)
Rework telemetry to replace the use of tracing with an object we pass around (#8143)
Decrease the peer reputation on invalid block requests (#8260)

Migrate pallet-indices to pallet! (#8465)
Migrate pallet-sudo to pallet! (#8448)
Upgrade pallet atomic swap (#8452)
Migrate pallet-utility to pallet attribute macro. (#8326)
contracts: Reduce the API surface (#8359)
Add tracing logic in pallet macro for hooks and dispatchables (#8305)
Use the log crate to output contract generated messages. (#8403)
Replace 'Module' with 'Pallet' in construct_runtime macro (#8372)
Migrate pallet-babe to pallet attribute macro. (#8310)
Migrate node authorization pallet to FRAME v2 (#8337)
Migrate pallet-proxy to pallet attribute macro (#8365)
im-online: use EstimateNextSessionRotation to get better estimates of session progress (#8242)
Add on_idle hook (#8209)
more clear randomness API for BABE (#8180)
Custom RPC for Merkle Mountain Range pallet (#8137)
pallet_macro: Generate default documentation for well known types (#8276)