Standardize address derivation

[ethanfrey]

Closes #410

[codecov]

Codecov Report

Merging #565 (4fbb945) into master (a012e00) will increase coverage by 0.05%.
The diff coverage is 92.00%.

❗ Current head 4fbb945 differs from pull request most recent head 6f720a4. Consider uploading reports for the commit 6f720a4 to get more accurate results

@@            Coverage Diff             @@
##           master     #565      +/-   ##
==========================================
+ Coverage   59.65%   59.71%   +0.05%     
==========================================
  Files          45       45              
  Lines        5260     5277      +17     
==========================================
+ Hits         3138     3151      +13     
- Misses       1892     1894       +2     
- Partials      230      232       +2     

Impacted Files	Coverage Δ
x/wasm/keeper/keeper.go	85.11% <90.47%> (-0.28%)	⬇️
x/wasm/types/test_fixtures.go	95.12% <100.00%> (ø)

[webmaster128]

Very nice. The derives addresses match my implementation in cosmos/cosmjs#857

Only the modularity point below. We use ADR-20 and truncate its output instead of having a different implementation, which makes things much nicer.