treewide: rename version attributes

As suggested in https://github.com/NixOS/nixpkgs/pull/39416#discussion_r183845745
the versioning attributes in `lib` should be consistent to
`nixos/version` which implicates the following changes:

* `lib.trivial.version` -> `lib.trivial.release`
* `lib.trivial.suffix` -> `lib.trivial.versionSuffix`
* `lib.nixpkgsVersion` -> `lib.version`

As `lib.nixpkgsVersion` is referenced several times in `NixOS/nixpkgs`,
`NixOS/nix` and probably several user's setups. As the rename will cause
a notable impact it's better to keep `lib.nixpkgsVersion` as alias with
a warning yielded by `builtins.trace`.

doc/Makefile

@@ -64,7 +64,7 @@ manual-full.xml: ${MD_TARGETS} .version *.xml
 
 .version:
 	nix-instantiate --eval \
-		-E '(import ../lib).nixpkgsVersion' > .version
+		-E '(import ../lib).version' > .version
 
 %.section.xml: %.section.md
 	pandoc $^ -w docbook+smart \