Bump trie-db to 0.20.0 (paritytech#79)

* Bump trie-db to 0.20.0

- Prefix iterator. [paritytech#39](paritytech#39)

* WIP

Bump trie-db to 0.20.0 (paritytech#79)

* Bump trie-db to 0.20.0

- Prefix iterator. [paritytech#39](paritytech#39)

* WIP

Bump trie-db to 0.20.0 (paritytech#79)

* Bump trie-db to 0.20.0

- Prefix iterator. [paritytech#39](paritytech#39)

* WIP

Bump trie-db to 0.20.0 (paritytech#79)

* Bump trie-db to 0.20.0

- Prefix iterator. [paritytech#39](paritytech#39)

* WIP

Bump trie-db to 0.20.0 (paritytech#79)

* Bump trie-db to 0.20.0

- Prefix iterator. [paritytech#39](paritytech#39)

* WIP

trie-db cleanup (paritytech#70)

* trie-db: remove unused rand feature

* trie-db: update to 2018 edition

* trie-db: use hashbrown for both std and no_std

* trie-db: update docs to 2018 edition

* trie-db: update benches to 2018 edition

* trie-db: bump criterion to 0.3

* trie-db: rename core_ to rstd

* trie-db: proper namespace management, closes paritytech#54

* revert unrelated changes

update-codec

Update codec + new release of trie-bench

Fix no_std build for memory-db. (paritytech#20)

Fix no_std build for memory-db

Merge pull request paritytech#14 from cheme/deprecate_heapsize

Deprecate heapsize

Merge pull request paritytech#18 from paritytech/ao-fix-trie-standard…

…map-deps

[trie-standardmap] remove unused dep; bump version to 0.12.3