Document file system object content addressing

In addition:

- Take the opportunity to add a bunch more missing hyperlinks, too.

- Remove some glossary entries that are now subsumed by dedicated pages.
  We used to not be able to do this without breaking link fragments, but
  now we can, so pick up where we left off.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

src/libstore/globals.hh

@@ -910,7 +910,7 @@ public:
         "substituters",
         R"(
           A list of [URLs of Nix stores](@docroot@/store/types/index.md#store-url-format) to be used as substituters, separated by whitespace.
-          A substituter is an additional [store](@docroot@/glossary.md#gloss-store) from which Nix can obtain [store objects](@docroot@/glossary.md#gloss-store-object) instead of building them.
+          A substituter is an additional [store](@docroot@/glossary.md#gloss-store) from which Nix can obtain [store objects](@docroot@/store/store-object.md) instead of building them.
 
           Substituters are tried based on their priority value, which each substituter can set independently.
           Lower value means higher priority.

src/libstore/path.hh

@@ -13,7 +13,7 @@ struct Hash;
  * \ref StorePath "Store path" is the fundamental reference type of Nix.
  * A store paths refers to a Store object.
  *
- * See glossary.html#gloss-store-path for more information on a
+ * See store/store-path.html for more information on a
  * conceptual level.
  */
 class StorePath