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.

tests/new/fail/match_missing_variant.fch

@@ -0,0 +1,10 @@
+// expect: doesn't handle Blue
+enum Color { Red, Green, Blue }
+
+fn main() {
+    c := Color.Red
+    match c {
+        Red -> print(1)
+        Green -> print(2)
+    }
+}