feat(furc): introduce native and import functions

Closes: #19

furc/include/furc/front/token.hpp

@@ -153,6 +153,8 @@ enum class keyword_token {
     If,     /**< `if` */
     Else,   /**< `else` */
     While,  /**< `while` */
+    Import, /**< `import` */
+    Native, /**< `native` */
 
     Int32, /**< `int32` */
 };
@@ -165,6 +167,8 @@ static inline std::ostream& operator<<(std::ostream& os, keyword_token keyword)
     case keyword_token::If: return os << "if";
     case keyword_token::Else: return os << "else";
     case keyword_token::While: return os << "while";
+    case keyword_token::Import: return os << "import";
+    case keyword_token::Native: return os << "native";
     case keyword_token::Int32: return os << "int32";
     }
     return os;
@@ -178,6 +182,8 @@ static inline std::string operator+(const std::string& str, keyword_token keywor
     case keyword_token::If: return str + "if";
     case keyword_token::Else: return str + "else";
     case keyword_token::While: return str + "while";
+    case keyword_token::Import: return str + "import";
+    case keyword_token::Native: return str + "native";
     case keyword_token::Int32: return str + "int32";
     }
     return str;