[DOC] Fix yet another dead link to Ragel

And extract the same links to a footnote.

README-json-jruby.md

@@ -23,7 +23,7 @@ Its path must be set on the `jruby.dir` property of
 `nbproject/project.properties` (defaults to `../jruby`).
 
 Additionally, you'll need [Ant](http://ant.apache.org/), and
-[Ragel](http://www.cs.queensu.ca/~thurston/ragel/) 6.4 or greater.
+[Ragel](http://www.colm.net/open-source/ragel/) 6.4 or greater.
 
 Then, from the folder where the sources are located, type:
 

README.md

@@ -12,8 +12,7 @@ will be two variants available:
   extensions, which are both part of the ruby standard library.
 * The quite a bit faster native extension variant, which is in parts
   implemented in C or Java and comes with its own unicode conversion
-  functions and a parser generated by the ragel state machine compiler
-  http://www.colm.net/open-source/ragel/ .
+  functions and a parser generated by the [Ragel] state machine compiler.
 
 Both variants of the JSON generator generate UTF-8 character sequences by
 default. If an :ascii\_only option with a true value is given, they escape all
@@ -71,8 +70,7 @@ with:
 ## Compiling the extensions yourself
 
 If you want to create the `parser.c` file from its `parser.rl` file or draw nice
-graphviz images of the state machines, you need ragel from:
-http://www.colm.net/open-source/ragel/
+graphviz images of the state machines, you need [Ragel].
 
 ## Usage
 
@@ -423,3 +421,5 @@ The latest version of this library can be downloaded at
 Online Documentation should be located at
 
 * https://www.rubydoc.info/gems/json
+
+[Ragel]: http://www.colm.net/open-source/ragel/