Fixes inability to deleteWordBackward at line start (#2046)

* Adds Unicode LF character to line endings for clipboard plaintext

This addresses https://github.com/ianstormtaylor/slate/issues/1932

* Fixes plaintext/unicode pastes not having line breaks

* Removes stray spaces for Prettier

* Refactors Value creation to save 4 lines

* Allows for Ctrl+Backspace on line start

Previously Ctrl+Backspace would do nothing instead of continuing on to the above block.

* Tests that deleteWordBackwards joins lines properly

packages/slate/src/changes/at-range.js

@@ -322,7 +322,7 @@ Changes.deleteWordBackwardAtRange = (change, range, options) => {
   const offset = startBlock.getOffset(start.key)
   const o = offset + start.offset
   const { text } = startBlock
-  const n = TextUtils.getWordOffsetBackward(text, o)
+  const n = o === 0 ? 1 : TextUtils.getWordOffsetBackward(text, o)
   change.deleteBackwardAtRange(range, n, options)
 }
 

packages/slate/test/changes/at-current-range/delete-word-backward/join-blocks.js

@@ -0,0 +1,28 @@
+/** @jsx h */
+
+import h from '../../../helpers/h'
+
+export default function(change) {
+  change.deleteWordBackward()
+}
+
+export const input = (
+  <value>
+    <document>
+      <paragraph>word</paragraph>
+      <paragraph>
+        <cursor />another
+      </paragraph>
+    </document>
+  </value>
+)
+
+export const output = (
+  <value>
+    <document>
+      <paragraph>
+        word<cursor />another
+      </paragraph>
+    </document>
+  </value>
+)