doc: Update keywords.txt with modern list of keywords derived from parser.

doc/keywords.txt

@@ -2,19 +2,19 @@
 
 alt any as assert
 be bind block bool break
-char check claim const cont
+char check claim class const cont copy crust
 do
-else export
+else enum export
 f32 f64 fail false float fn for
-i16 i32 i64 i8 if import in int
+i16 i32 i64 i8 if iface impl import in int
 let log loop
-mod mut
-native note
+mod move mut
+native new
 obj  
-prove pure
+priv pure
 resource ret
-self str syntax
-tag true type
+self send str
+tag to trait true type
 u16 u32 u64 u8 uint unchecked unsafe use
 vec
 while with