Escaped characters in alt text of image links are now unescaped

This fixes #135 insofar that there is a working solution by
escaping the pipe characters.

lib/kramdown/converter/kramdown.rb

@@ -285,16 +285,17 @@ def convert_a(el, opts)
       end
 
       def convert_img(el, opts)
+        alt_text = el.attr['alt'].gsub(ESCAPED_CHAR_RE) { $1 ? "\\#{$1}" : $2 }
         if el.attr['src'].empty?
-          "![#{el.attr['alt']}]()"
+          "![#{alt_text}]()"
         else
           title = (el.attr['title'] ? ' "' + el.attr['title'].gsub(/"/, """) + '"' : '')
           link = if el.attr['src'].count("()") > 0
                    "<#{el.attr['src']}>"
                  else
                    el.attr['src']
                  end
-          "![#{el.attr['alt']}](#{link}#{title})"
+          "![#{alt_text}](#{link}#{title})"
         end
       end
 

lib/kramdown/parser/kramdown/link.rb

@@ -7,6 +7,8 @@
 #++
 #
 
+require 'kramdown/parser/kramdown/escaped_chars'
+
 module Kramdown
   module Parser
     class Kramdown
@@ -76,7 +78,7 @@ def parse_link
           add_text(result)
           return
         end
-        alt_text = extract_string(reset_pos...@src.pos, @src)
+        alt_text = extract_string(reset_pos...@src.pos, @src).gsub(ESCAPED_CHARS, '\1')
         @src.scan(LINK_BRACKET_STOP_RE)
 
         # reference style link or no link url

test/testcases/span/01_link/imagelinks.html

@@ -12,3 +12,4 @@
 
 <p>No id: <img src="other.png" alt="imgo" title="Title" /></p>
 
+<p>With escaped pipe: <img src="other.png" alt="an | pipe" /></p>

test/testcases/span/01_link/imagelinks.text

@@ -14,3 +14,5 @@ No id: ![imgo]
 
 [img]: other.png
 [imgo]: other.png "Title"
+
+With escaped pipe: ![an \| pipe](other.png)