feat: support fallible results and scoped cleanup

source/lexer/scan.hon

@@ -26,6 +26,10 @@ keywords strmap.StaticStringMap(TokenKind) :: strmap.init([
     { "return", .return },
     { "break", .break },
     { "continue", .continue },
+    { "try", .try },
+    { "catch", .catch },
+    { "defer", .defer },
+    { "errdefer", .errdefer },
     { "if", .if },
     { "for", .for },
     { "else", .else },

source/lexer/token.hon

@@ -23,6 +23,8 @@ TokenKind :: enum {
     match
     proc, return
     break, continue
+    try, catch
+    defer, errdefer
     true, false
     and, or
     struct, enum, union