Favor GFM-style relative markdown links.

doc/callbacks.md

@@ -21,7 +21,9 @@ your platform uses mawk, see below).
 <name a="library"></a>
 ## Library
 
-This repository includes a [library](doc/library.md) of awk callbacks that were
+This repository includes a
+[library](https://github.com/step-/JSON.awk/blob/master/doc/library.md)
+of awk callbacks that were
 developed to solve various practical problems, and are fully worked-out source
 code examples of how to use the callback interface.
 
@@ -34,7 +36,8 @@ To use callbacks an application must:
 
 2. define the callback functions.
 
-File [callbacks.awk](callbacks.awk) implements stubs of all required
+File [callbacks.awk](https://github.com/step-/JSON.awk/blob/master/callbacks.awk)
+implements stubs of all required
 callback functions that your application can reuse or redefine as needed.
 
 When `STREAM=0` JSON.awk will modify its behavior as follows: