Strictness

[jennyzzz]

[x] awesome-code-style
[x] Run all linters in tests
[x] strictNullChecks: true
[x] strict: true
[x] noUnusedParameters : true
[x] noUnusedLocals : true
[x] esModuleInterop: true
[ ] No TDI (** see marks below)
[ ] Jest (%%% see marks below)

%%%
For Jest, I added 2 of 4 tests into Jest tests, and they passed. However, the other 2 mocha tests failed even before transferring to Jest. So I just keep the 2 mocha tests as is for now. Here is the mocha tests' failure log:

**
For TDI, some of the types we use from tdi are different from what I could get from @types/....
For example, for stream-json lib, the types from @types/stream-json (https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/stream-json/index.d.ts) are different from what we have in tdi (https://github.com/implydata/tdi/blob/master/typings/stream-json/index.d.ts).
Another example is readable-stream lib. Type ReadableStream exists in tdi (https://github.com/implydata/tdi/blob/master/typings/readable-stream/index.d.ts), but not in @types.readable-stream (https://github.com/DefinitelyTyped/DefinitelyTyped/blob/36ddc60d7c4734d6c6593d1ab3273b72afae68ef/types/readable-stream/index.d.ts).
So I didn't delete tdi in this repo.