enums and match (in the compiler written in Finch)

enum Color { Red, Green, Blue }   enum Status { Ok = 200, NotFound = 404 }

Color.Red, Color(n) (checked), int(c), == and != only, printed by name, usable as
map keys and struct fields, with methods (fn Color.next()).

match value { Red, Green -> ... Blue -> ... else -> ... } as a statement, or as an
expression that gives a value. Works on enums, whole numbers, chars, text and bools;
a match on an enum has to handle every variant or end with else, and says which are
missing. A bare variant name (Red) is enough inside a match on an enum.

Only the self-hosted compiler has them; tests/new holds their tests, tests/run stays what
the C++ compiler also runs. boot.sh: 31 passed.

boot/lexer.fch

@@ -24,7 +24,7 @@ fn isHex(char c) -> bool {
 
 fn isKeyword(str w) -> bool {
     keywords := ["fn", "return", "if", "else", "while", "for", "in", "break", "continue", "true", "false",
-                 "null", "import", "link", "struct", "defer", "or", "try"]
+                 "null", "import", "link", "struct", "defer", "or", "try", "enum", "match"]
     return keywords.contains(w)
 }