py: Support unicode (utf-8 encoded) identifiers in Python source.

Enabled simply by making the identifier lexing code 8-bit clean.

tests/unicode/unicode_id.py

@@ -0,0 +1,27 @@
+# test unicode in identifiers
+
+# comment
+# αβγδϵφζ
+
+# global identifiers
+α = 1
+αβγ = 2
+bβ = 3
+βb = 4
+print(α, αβγ, bβ, βb)
+
+# function, argument, local identifiers
+def α(β, γ):
+    δ = β + γ
+    print(β, γ, δ)
+α(1, 2)
+
+# class, method identifiers
+class φ:
+    def __init__(self):
+        pass
+    def δ(self, ϵ):
+        print(ϵ)
+zζzζz = φ()
+if hasattr(zζzζz, "δ"):
+    zζzζz.δ(ϵ=123)