refactor RCCL (#1112)

* refactor RCCL

* rccl updates

* Update index.rst

* refactor

* Update what-is-rccl.rst

[ROCm/rccl commit: 45ee5734dd]

projects/rccl/docs/sphinx/_toc.yml.in

@@ -1,10 +1,15 @@
 root: index
 subtrees:
 - entries:
-  - file: api
-  - file: allapi
-  - file: attributions
+  - file: what-is-rccl
+- caption: API reference 
+  entries:
+  - file: library-specification
+    title: Library specification
+  - file: api-library
+  
 - caption: About
   entries:
   - file: license
+  - file: attributions