Fixes #52.

This PR provides bundles compatible with ES5 + ES2015 modules (instead of UMD / CommonJS).
This allows tools like Webpack to work without requiring a separate Babel-enabled compilation step or other expensive setup.

Unfortunately we cannot add ES5 as the default build indicated by the module entry in package.json, therefore the default build remains the ES2015 build. This is because:

1. the ES5 compatibility requirement is only temporary, current versions of Firefox, Chrome and Safari already support all of ES2015, see: https://kangax.github.io/compat-table/es6/
2. ES5 code loses info that could be used by minifiers and has auto-generated junk in it for supporting features (e.g. class inheritance, async generators, etc.) which can generate conflicts

The solution is to provide a separate ES5 build that can be used like this when doing a la carte dependency management:

// funfix-core
import { Option } from "funfix-core/dist/es5"

// funfix-exec
import { Future } from "funfix-exec/dist/es5"

// funfix-effect
import { IO } from "funfix-effect/dist/es5"

// funfix-types
import { Monad } from "funfix-types/dist/es5"

Note that because of the way the TypeScript / JavaScript toolchain works, you may experience issues, because when doing testing with Mocha or Jest by means of say ts-node, the ES2015 imports end up using CommonJS under the hood (since they are running on top of Node) and thus don't expect ES2015 modules.

Or you can see weird type mismatch errors, the compiler seeing the same type name imported from different places. An easy fix for this particular issue is to use the main funfix dependency, which includes everything in the UMD and ES5 bundles:

import * as ff from "funfix/dist/es5"

All of this isn't the fault of Funfix, but of the way the JS tool-chain works. If you experience issues, drop on the Gitter channel to see what we can do.

Welcome to the hell that is JavaScript dependency management! This PR fixes one issue related to it. Probably more to come.