fp-ts bindings for rxjs

Implemented instances

- Monad
- Alternative
- Filterable

Example

``ts
import { from } from 'rxjs'
import { observable } from 'fp-ts-rxjs/Observable'

const fa = from([1, 2, 3])
const fb = observable.chain(fa, a => from([a, a + 1]))
// fb will emit 1, 2, 2, 3, 3, 4
`

TypeScript compatibility

The stable version is tested against TypeScript 3.1.3

rxjs compatibility

| rxjs version | fp-ts-\* version |
| ------------ | ---------------------- |
| rxjs@7 | fp-ts-reactive@0.6.x |
| rxjs@6 | fp-ts-rxjs@0.5.x |
| rxjs@5 | fp-ts-rxjs@0.4.x` |