Add support for number type in attributes

Closes GH-5.

Reviewed-by: Christian Murphy <christian.murphy.42@gmail.com>
Reviewed-by: Titus Wormer <tituswormer@gmail.com>

Author: malav2110

types/index.d.ts

@@ -1,8 +1,15 @@
 // TypeScript Version: 3.7
 
-import {Attributes, Element, Node} from 'xast'
+import {Element, Node} from 'xast'
 
-type Children = string | Node | Children[]
+type Children = string | Node | number | Children[]
+
+type Primitive = null | undefined | string | number
+
+/**
+ * Extending Attributes to Support JS Primitive Types
+ */
+type Attributes = Record<string, Primitive>
 
 /**
  * Create XML trees in xast.

types/test.ts

@@ -15,11 +15,18 @@ x('urlset', {xmlns}) // $ExpectType Element
 x('urlset', {xmlns}, 'string') // $ExpectType Element
 x('urlset', {xmlns}, ['string', 'string']) // $ExpectType Element
 x('urlset', {xmlns}, x('loc'), 'string') // $ExpectType Element
+x('urlset', {xmlns}, x('loc'), 100) // $ExpectType Element
 x('urlset', {xmlns}, x('loc')) // $ExpectType Element
 x('urlset', {xmlns}, x('loc'), x('loc')) // $ExpectType Element
 x('urlset', {xmlns}, [x('loc'), x('loc')]) // $ExpectType Element
 x('urlset', {xmlns}, []) // $ExpectType Element
 
+const xmlNumberAttribute = 100
+x('urlset', {xmlNumberAttribute}, 'string') // $ExpectType Element
+x('urlset', {xmlNumberAttribute}, 100) // $ExpectType Element
+x('urlset', {xmlNumberAttribute}, x('loc'), 100) // $ExpectType Element
+x('urlset', {xmlNumberAttribute}, []) // $ExpectType Element
+
 x() // $ExpectError
 x(false) // $ExpectError
 x('urlset', x('loc'), {xmlns}) // $ExpectError