Allow to forward declare of public structs #1215

Thanks to forward declare we can declare `struct` in our header file instead making #include
diff --git a/include/mbedtls/ssl_ticket.h b/include/mbedtls/ssl_ticket.h
index 93ad46a..b2686df 100644
--- a/include/mbedtls/ssl_ticket.h
+++ b/include/mbedtls/ssl_ticket.h
@@ -44,7 +44,7 @@
 /**
  * \brief   Information for session ticket protection
  */
-typedef struct
+typedef struct mbedtls_ssl_ticket_key
 {
     unsigned char name[4];          /*!< random key identifier              */
     uint32_t generation_time;       /*!< key generation timestamp (seconds) */
@@ -55,7 +55,7 @@
 /**
  * \brief   Context for session ticket handling functions
  */
-typedef struct
+typedef struct mbedtls_ssl_ticket_context
 {
     mbedtls_ssl_ticket_key keys[2]; /*!< ticket protection keys             */
     unsigned char active;           /*!< index of the currently active key  */