doc: Follow the current naming convention.

src/pki.c

@@ -21,7 +21,7 @@
  */
 
 /**
- * @defgroup libssh_pki SSH Public Key Infrastructure
+ * @defgroup libssh_pki The SSH Public Key Infrastructure
  * @ingroup libssh
  *
  * Functions for the creation, importation and manipulation of public and

src/threads.c

@@ -20,7 +20,7 @@
  */
 
 /**
- * @defgroup libssh_threads Threading with libssh
+ * @defgroup libssh_threads The SSH threading functions.
  * @ingroup libssh
  *
  * Threading with libssh