Allow recursive includes (#7)

plugins/include-markdown/fixtures/basic.expected.md

@@ -1,9 +1,11 @@
 hello this is a file that uses an include
 
-hi i come from an **included file**
+include/before
 
-yay!
+nested/include2
 
-I come from a nested folder
+include/after
+
+nested/include2
 
 isn't that neat?

plugins/include-markdown/fixtures/include.md

@@ -1,3 +1,5 @@
-hi i come from an **included file**
+include/before
 
-yay!
+@include 'nested/include2.md'
+
+include/after

plugins/include-markdown/fixtures/nested/include2.md

@@ -1 +1 @@
-I come from a nested folder
+nested/include2

plugins/include-markdown/fixtures/nested/include3.md

@@ -0,0 +1,3 @@
+nested/include3
+
+@include 'include2.md'

plugins/include-markdown/fixtures/resolve-from.expected.md

@@ -1 +1,3 @@
-I come from a nested folder
+nested/include3
+
+nested/include2

plugins/include-markdown/fixtures/resolve-from.md

@@ -1 +1 @@
-@include 'include2.md'
+@include 'include3.md'

plugins/include-markdown/index.js

@@ -21,16 +21,18 @@ module.exports = function includeMarkdownPlugin({ resolveFrom } = {}) {
       )
       let includeContents
       try {
-        includeContents = readSync(includePath)
+        includeContents = readSync(includePath, 'utf8')
       } catch (err) {
         throw new Error(
           `The @include file path at ${includePath} was not found.\n\nInclude Location: ${file.path}:${node.position.start.line}:${node.position.start.column}`
         )
       }
 
       // return the file contents in place of the @include
-
-      return remark().parse(includeContents).children
+      // this takes a couple steps because we allow recursive includes
+      const processor = remark().use(includeMarkdownPlugin, { resolveFrom })
+      const ast = processor.parse(includeContents)
+      return processor.runSync(ast, includeContents).children
     })
   }
 }