Add prettier as a YAML option (#1789)

* Add prettier as a yaml fixer

* Sort yaml fixers alphabetically

* Add prettier to doc/ale.txt

* Add ale-yaml-prettier

* Add ale-yaml-prettier to the TOC

README.md

@@ -190,7 +190,7 @@ formatting.
 | Vue | [prettier](https://github.com/prettier/prettier), [vls](https://github.com/vuejs/vetur/tree/master/server) |
 | XHTML | [alex](https://github.com/wooorm/alex) !!, [proselint](http://proselint.com/), [write-good](https://github.com/btford/write-good) |
 | XML | [xmllint](http://xmlsoft.org/xmllint.html) |
-| YAML | [swaglint](https://github.com/byCedric/swaglint), [yamllint](https://yamllint.readthedocs.io/) |
+| YAML | [prettier](https://github.com/prettier/prettier), [swaglint](https://github.com/byCedric/swaglint), [yamllint](https://yamllint.readthedocs.io/) |
 | YANG | [yang-lsp](https://github.com/theia-ide/yang-lsp) |
 
 <a name="usage"></a>

doc/ale-yaml.txt

@@ -1,6 +1,20 @@
 ===============================================================================
 ALE YAML Integration                                         *ale-yaml-options*
 
+===============================================================================
+prettier                                                    *ale-yaml-prettier*
+
+Website: https://github.com/prettier/prettier
+
+
+Installation
+-------------------------------------------------------------------------------
+
+Install prettier either globally or locally: >
+
+  npm install prettier -g  # global
+  npm install prettier     # local
+<
   
 ===============================================================================
 swaglint                                                    *ale-yaml-swaglint*

doc/ale.txt

@@ -290,6 +290,7 @@ CONTENTS                                                         *ale-contents*
     xml...................................|ale-xml-options|
       xmllint.............................|ale-xml-xmllint|
     yaml..................................|ale-yaml-options|
+      prettier............................|ale-yaml-prettier|
       swaglint............................|ale-yaml-swaglint|
       yamllint............................|ale-yaml-yamllint|
     yang..................................|ale-yang-options|
@@ -436,7 +437,7 @@ Notes:
 * Vue: `prettier`, `vls`
 * XHTML: `alex`!!, `proselint`, `write-good`
 * XML: `xmllint`
-* YAML: `swaglint`, `yamllint`
+* YAML: `prettier`, `swaglint`, `yamllint`
 * YANG: `yang-lsp`
 
 ===============================================================================