feat: finish env remains functions

src/yycc/env.hpp

@@ -72,6 +72,7 @@ namespace yycc::env {
      * @brief Returns an list of (variable, value) pairs of strings, 
      * for all the environment variables of the current process.
      * @return The list holding all variables.
+     * @exception std::runtime_error Error occurs when getting variables.
      */
     std::vector<VarPair> get_vars();
 
@@ -131,6 +132,7 @@ namespace yycc::env {
     /**
      * @brief Returns the arguments that this program was started with (normally passed via the command line).
      * @return The list holding all argument one by one.
+     * @exception std::runtime_error Error occurs when getting arguments.
      */
     std::vector<std::u8string> get_args();