feat: provide named exports api (jquense#1348)

BREAKING CHANGE: must use named exports for additional RBC imports

```js
import {
  Calendar,
  DateLocalizer,
  momentLocalizer,
  globalizeLocalizer,
  move,
  Views,
  Navigate,
  components
} from 'react-big-calendar';
```

.size-snapshot.json

@@ -1,25 +1,25 @@
 {
   "./dist/react-big-calendar.js": {
-    "bundled": 553987,
-    "minified": 170205,
-    "gzipped": 50025
+    "bundled": 554087,
+    "minified": 170209,
+    "gzipped": 49950
   },
   "./dist/react-big-calendar.min.js": {
-    "bundled": 490228,
-    "minified": 150810,
-    "gzipped": 45487
+    "bundled": 490328,
+    "minified": 150824,
+    "gzipped": 45415
   },
   "dist/react-big-calendar.esm.js": {
-    "bundled": 169712,
-    "minified": 81562,
-    "gzipped": 20075,
+    "bundled": 169648,
+    "minified": 81524,
+    "gzipped": 20082,
     "treeshaked": {
       "rollup": {
-        "code": 62970,
+        "code": 59035,
         "import_statements": 1402
       },
       "webpack": {
-        "code": 66409
+        "code": 62470
       }
     }
   }

README.md

@@ -39,14 +39,14 @@ Regardless of your choice, you **must** choose a localizer to use this library:
 #### Moment.js
 
 ```js
-import BigCalendar from 'react-big-calendar'
+import { Calendar, momentLocalizer } from 'react-big-calendar'
 import moment from 'moment'
 
-const localizer = BigCalendar.momentLocalizer(moment)
+const localizer = momentLocalizer(moment)
 
 const MyCalendar = props => (
   <div>
-    <BigCalendar
+    <Calendar
       localizer={localizer}
       events={myEventsList}
       startAccessor="start"
@@ -59,14 +59,14 @@ const MyCalendar = props => (
 #### Globalize.js v0.1.1
 
 ```js
-import BigCalendar from 'react-big-calendar'
+import { Calendar, globalizeLocalizer } from 'react-big-calendar'
 import globalize from 'globalize'
 
-const localizer = BigCalendar.globalizeLocalizer(globalize)
+const localizer = globalizeLocalizer(globalize)
 
 const MyCalendar = props => (
   <div>
-    <BigCalendar
+    <Calendar
       localizer={localizer}
       events={myEventsList}
       startAccessor="start"

src/index.js

@@ -1,24 +1,15 @@
-import Calendar from './Calendar'
 import EventWrapper from './EventWrapper'
 import BackgroundWrapper from './BackgroundWrapper'
-import { DateLocalizer } from './localizer'
-import momentLocalizer from './localizers/moment'
-import globalizeLocalizer from './localizers/globalize'
-import move from './utils/move'
-import { views, navigate } from './utils/constants'
 
-Object.assign(Calendar, {
-  DateLocalizer,
-  globalizeLocalizer,
-  momentLocalizer,
-  Views: views,
-  Navigate: navigate,
-  move,
-  components: {
-    eventWrapper: EventWrapper,
-    timeSlotWrapper: BackgroundWrapper,
-    dateCellWrapper: BackgroundWrapper,
-  },
-})
+export const components = {
+  eventWrapper: EventWrapper,
+  timeSlotWrapper: BackgroundWrapper,
+  dateCellWrapper: BackgroundWrapper,
+}
 
-export default Calendar
+export { default as Calendar } from './Calendar'
+export { DateLocalizer } from './localizer'
+export { default as momentLocalizer } from './localizers/moment'
+export { default as globalizeLocalizer } from './localizers/globalize'
+export { default as move } from './utils/move'
+export { views as Views, navigate as Navigate } from './utils/constants'