Fix headers in Doxygen output.

include/api.hpp

@@ -31,12 +31,14 @@ using std::variant;
  *  @brief  Holds API endpoints.
  *
  *  @since  0.1.0
+ *
+ *  @headerfile api.hpp mastodonpp/api.hpp
  */
 class API
 {
 public:
     /*!
-     *  @brief  An enumeration of all v1 API endpoints.
+     *  @brief  An enumeration of all v1 %API endpoints.
      *
      *  The original `/` are substituted with `_`.
      *
@@ -48,7 +50,7 @@ public:
     };
 
     /*!
-     *  @brief  An enumeration of all v2 API endpoints.
+     *  @brief  An enumeration of all v2 %API endpoints.
      *
      *  The original `/` are substituted with `_`.
      *

include/exceptions.hpp

@@ -34,6 +34,8 @@ using std::string;
  *  @brief  Exception for libcurl errors.
  *
  *  @since  0.1.0
+ *
+ *  @headerfile exceptions.hpp mastodonpp/exceptions.hpp
  */
 class CURLException : public exception
 {

include/instance.hpp

@@ -30,6 +30,8 @@ using std::string;
  *  @brief  Holds the hostname and access token of an instance.
  *
  *  @since  0.1.0
+ *
+ *  @headerfile instance.hpp mastodonpp/instance.hpp
  */
 class Instance
 {

include/mastodonpp.hpp

@@ -24,6 +24,8 @@
 #include "return_types.hpp"
 
 /*!
+ *  @headerfile mastodonpp.hpp mastodonpp/mastodonpp.hpp
+ *
  *  @mainpage mastodonpp Reference
  *
  *  @section using Using the library

include/request.hpp

@@ -32,6 +32,8 @@ using std::string;
  *  @brief  Used to make a request to the Mastodon API.
  *
  *  @since  0.1.0
+ *
+ *  @headerfile request.hpp mastodonpp/request.hpp
  */
 class Request
 {

include/return_types.hpp

@@ -34,6 +34,8 @@ using std::string_view;
  *
  *  @since  0.1.0
  *
+ *  @headerfile return_types.hpp mastodonpp/return_types.hpp
+ *
  *  @section error Error codes
  *  |      Code | Explanation                                                  |
  *  | --------: |:-------------------------------------------------------------|