Update CHANGELOG for v2.0.1 release. (dgraph-io#1181)

(cherry picked from commit 23a73cd)

Rename option builder from WithInmemory to WithInMemory. (dgraph-io#1169

)

The name of the option builder func should be spelled the same as the
option name itself.

The godoc already has the func documented as "WithInMemory".

Update changelog for v2.0.0. (dgraph-io#1117)

Badger v2.0.0-rc4

adapt import paths for v2

Add Ibrahim to code owners (dgraph-io#978)

Explaining new version naming schema. (dgraph-io#906)

* Explaining new Serialization Versioning schema used in Badger.

adding Go Modules back

updated CHANGELOG to include new Options API

Merge pull request dgraph-io#882 from dgraph-io/v2mod

release badger v2.0.0