Full support of no_std in tendermint crate

[soareschen]

Part of informalsystems/hermes#1158.

This PR builds on #980 and #986. Either the two PRs can be merged separately first, or we can merge them together here in one go.

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[xla]

Can we set the base to the dependent PR? This would make it easier to review the change. Otherwise it's interleaved with unrelated changes.

[soareschen]

Can we set the base to the dependent PR? This would make it easier to review the change. Otherwise it's interleaved with unrelated changes.

This PR is really just a merge of both #980 and #986 with an additional commit f07d0c0. So you can just look at that in the meanwhile. After the other PRs we can update this branch again for a cleaner diff.

[codecov-commenter]

Codecov Report

Merging #988 (27a3ed3) into master (9690eca) will decrease coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff            @@
##           master    #988     +/-   ##
========================================
- Coverage    66.1%   66.0%   -0.1%     
========================================
  Files         209     209             
  Lines       20764   20760      -4     
========================================
- Hits        13726   13720      -6     
- Misses       7038    7040      +2     

Impacted Files	Coverage Δ
config/src/config.rs	55.0% <ø> (-1.5%)	⬇️
light-client/src/lib.rs	100.0% <ø> (ø)
proto/src/lib.rs	100.0% <ø> (ø)
tendermint/src/lib.rs	100.0% <ø> (ø)
tendermint/src/signature.rs	55.0% <ø> (+0.5%)	⬆️
tendermint/src/proposal.rs	90.4% <100.0%> (-0.3%)	⬇️
tendermint/src/test.rs	100.0% <100.0%> (ø)
tendermint/src/vote.rs	76.6% <100.0%> (+0.3%)	⬆️
tendermint/src/vote/sign_vote.rs	96.5% <100.0%> (ø)
testgen/src/vote.rs	84.8% <100.0%> (+0.8%)	⬆️
... and 8 more

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[xla]

This PR is really just a merge of both #980 and #986 with an additional commit f07d0c0. So you can just look at that in the meanwhile. After the other PRs we can update this branch again for a cleaner diff.

Thanks for the clarification, let's set it to Draft to indicate that crucial prerequisites are not in place yet.

[soareschen]

This is now fixed by #1087.