v20.2.0

features added:

• added an LRU cache over unboxer
• added mac + win test to travis
• modify addBoxer to take an init method, modify db methods to wait for boxer initialisation (where required)

fixes / maintenance:

• fixed test suite so all tests are running + passing
• refactored some tests + clearly named all tests
• updated some deps : mkdirp, flumedb, ssb-ref, tape