Some minor improvements to the yaml-metadata docs

Switching form XAML to YAML syntax highlighting and fixing some grammar.

Signed-off-by: Sheogorath <[email protected]>

Author: SISheogorath

public/docs/yaml-metadata.md

@@ -25,7 +25,7 @@ This option will set the note title which prior than content title.
 > default: not set
 
 **Example**
-```xml
+```yml
 title: meta title
 ```
 
@@ -36,7 +36,7 @@ This option will set the note description.
 > default: not set
 
 **Example**
-```xml
+```yml
 description: meta description
 ```
 
@@ -47,7 +47,7 @@ This option will set the tags which prior than content tags.
 > default: not set
 
 **Example**
-```xml
+```yml
 tags: features, cool, updated
 ```
 
@@ -62,7 +62,7 @@ So you can prevent any search engine index your note by set `noindex, nofollow`.
 > default: not set
 
 **Example**
-```xml
+```yml
 robots: noindex, nofollow
 ```
 
@@ -75,21 +75,21 @@ https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes
 > default: not set (which will be en)
 
 **Example**
-```xml
+```yml
 langs: ja-jp
 ```
 
 dir
 ---
-This option provide to describe the direction of the text in this note.
+This option specifies the direction of the text in this note.
 You can only use whether `rtl` or `ltr`.
 Look more at here:
 http://www.w3.org/International/questions/qa-html-dir
 
 > default: not set (which will be ltr)
 
 **Example**
-```xml
+```yml
 dir: rtl
 ```
 
@@ -102,29 +102,29 @@ You can only use whether `true` or `false`.
 > default: not set (which will be true)
 
 **Example**
-```xml
+```yml
 breaks: false
 ```
 
 GA
 ---
-This option allow you to enable Google Analytics with your ID.
+This option allows you to enable Google Analytics with your ID.
 
 > default: not set (which won't enable)
 
 **Example**
-```xml
+```yml
 GA: UA-12345667-8
 ```
 
 disqus
 ---
-This option allow you to enable Disqus with your shortname.
+This option allows you to enable Disqus with your shortname.
 
 > default: not set (which won't enable)
 
 **Example**
-```xml
+```yml
 disqus: codimd
 ```
 
@@ -135,13 +135,13 @@ This option allows you to switch the document view to the slide preview, to simp
 > default: not set
 
 **Example:**
-```xml
+```yml
 type: slide
 ```
 
 slideOptions
 ---
-This option allow you provide custom options to slide mode.
+This option allows you to provide custom options to slide mode.
 Please below document for more details:
 https://github.com/hakimel/reveal.js/#configuration
 
@@ -153,7 +153,7 @@ https://github.com/hakimel/reveal.js/tree/master/css/theme
 > default: not set (which use default slide options)
 
 **Example**
-```xml
+```yml
 slideOptions:
   transition: fade
   theme: white