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/macros-spec.janet

@@ -0,0 +1,27 @@
+# Specification: macros, quoting and syntax-quote.
+(use ../support/harness)
+
+(defspec "macros / quoting"
+  ["quote symbol"       "(quote a)"         "(quote a)"]
+  ["quote list"         "[1 2 3]"     "(quote (1 2 3))"]
+  ["quote nested"       "[1 [2 3]]"   "(quote (1 (2 3)))"]
+  ["quote sugar"        "'a"          "'a"]
+  ["syntax-quote literal" "[1 2]"     "`[1 2]"]
+  ["unquote"            "[1 2 3]"     "(let [x 2] `[1 ~x 3])"]
+  ["unquote-splicing"   "[1 2 3 4]"   "(let [xs [2 3]] `[1 ~@xs 4])"]
+  ["unquote in list"    "[3]"         "(let [x 3] `(~x))"]
+  ["syntax-quote symbol qualifies" "true" "(symbol? `foo)"])
+
+(defspec "macros / defmacro"
+  ["simple macro"       "3"
+   "(do (defmacro m [a b] `(+ ~a ~b)) (m 1 2))"]
+  ["macro unless"       "1"
+   "(do (defmacro unless [c body] `(if ~c nil ~body)) (unless false 1))"]
+  ["macro with body splice" "6"
+   "(do (defmacro msum [& xs] `(+ ~@xs)) (msum 1 2 3))"]
+  ["macroexpand-1"      "true"
+   "(do (defmacro m [x] `(inc ~x)) (list? (macroexpand-1 '(m 5))))"]
+  ["gensym unique"      "false"
+   "(= (gensym) (gensym))"]
+  ["gensym# in template" "true"
+   "(do (defmacro m [] `(let [x# 1] x#)) (= 1 (m)))"])