test(spec): macros, reader, host-interop, namespaces — fix def-doc, resolve, %&

Final spec areas. Bugs caught and fixed:
- (def name docstring value) used the docstring as the value; now the 3-arg
  docstring form binds the value and records :doc meta
- resolve was a nil stub; now a special form resolving a symbol to its var
  (nil if unresolved). Added find-ns (non-creating lookup) and ns-name.
- in-ns didn't evaluate its arg, so (in-ns 'foo) failed; now evaluates it per
  Clojure (the integration test's unquoted form updated to the quoted idiom)
- #(... %& ...) built %& as a positional param instead of a & rest param;
  now emits (fn* [... & gen] ...) so %& captures the rest

Full public-API spec layer now in place. conformance 218/218, jpm test green.

test/spec/namespaces-spec.janet

@@ -0,0 +1,27 @@
+# Specification: namespaces, vars and require.
+(use ../support/harness)
+
+(defspec "namespaces / def & vars"
+  ["def + deref"        "5"        "(do (def x 5) x)"]
+  ["def returns var"    "true"     "(var? (def y 1))"]
+  ["declare then def"   "2"        "(do (declare z) (def z 2) z)"]
+  ["var special form"   "true"     "(var? (var +))"]
+  ["var sugar #'"       "true"     "(var? #'+)"]
+  ["var-get"            "5"        "(do (def w 5) (var-get #'w))"]
+  ["defn defines fn"    "3"        "(do (defn f [x] (inc x)) (f 2))"]
+  ["def with docstring" "7"        "(do (def d \"a doc\" 7) d)"])
+
+(defspec "namespaces / ns operations"
+  ["in-ns switches"     "true"     "(do (in-ns 'my.ns) (symbol? 'x))"]
+  ["ns-name"            "true"     "(do (require (quote [clojure.string])) (= 'clojure.string (ns-name (find-ns 'clojure.string))))"]
+  ["find-ns existing"   "true"     "(some? (find-ns 'clojure.core))"]
+  ["find-ns missing"    "nil"      "(find-ns 'does.not.exist)"]
+  ["resolve var"        "true"     "(var? (resolve '+))"]
+  ["resolve missing"    "nil"      "(resolve 'totally-undefined-xyz)"])
+
+(defspec "namespaces / require & refer"
+  ["require :as"        "\"AB\""   "(do (require '[clojure.string :as s]) (s/upper-case \"ab\"))"]
+  ["require :refer"     "true"     "(do (require '[clojure.string :refer [blank?]]) (blank? \"\"))"]
+  ["require :as + :refer" "true"   "(do (require '[clojure.string :as s :refer [blank?]]) (and (blank? \"\") (= \"X\" (s/upper-case \"x\"))))"]
+  ["require clojure.set" "#{1 2 3}" "(do (require '[clojure.set :as set]) (set/union #{1 2} #{3}))"]
+  ["require clojure.walk" "{:a 2}" "(do (require '[clojure.walk :as w]) (w/postwalk (fn [x] (if (number? x) (inc x) x)) {:a 1}))"])