Move resolve_tilde and get_config_path into libi3

include/libi3.h

@@ -434,3 +434,21 @@ char *get_exe_path(const char *argv0);
  *
  */
 int logical_px(const int logical);
+
+/**
+ * This function resolves ~ in pathnames.
+ * It may resolve wildcards in the first part of the path, but if no match
+ * or multiple matches are found, it just returns a copy of path as given.
+ *
+ */
+char *resolve_tilde(const char *path);
+
+/**
+ * Get the path of the first configuration file found. If override_configpath
+ * is specified, that path is returned and saved for further calls. Otherwise,
+ * checks the home directory first, then the system directory first, always
+ * taking into account the XDG Base Directory Specification ($XDG_CONFIG_HOME,
+ * $XDG_CONFIG_DIRS)
+ *
+ */
+char *get_config_path(const char *override_configpath, bool use_system_paths);