Make IsSuperMajority a standalone function
Move remaining CBlockIndex methods to chain.cpp
Fix download link for gitian builds
Merge pull request #5357

5ea3bc0 Move remaining CBlockIndex methods to chain.cpp (Pieter Wuille)
9dcd524 Make IsSuperMajority a standalone function (Pieter Wuille)
Merge pull request #5471

164a45f Fix download link for gitian builds (BtcDrak)
Create developer-notes.md

Moves coding guidelines and development tips/tricks into a single file.
Also adds a section explaining pull request terminology.