support type hints; make metadata coherent

The reader expanded ^X form to (with-meta form X), which evaluated the tag (so
^String errored 'Unable to resolve symbol: String') and, as a param, was no
longer a bare symbol (so the arg bound to nil). Now a keyword/symbol/string hint
on a symbol attaches to the symbol's :meta and the symbol stays bare, so type
hints are transparent in params, lets, and bodies. Map metadata still uses a
runtime with-meta form.

meta now returns a symbol's :meta, and def applies the name's metadata
(^:dynamic, ^:private, ^Type tag, ^{:doc}) to the var, so (meta (var x)) is
consistent. Specs in metadata-spec; grammar note in the ebnf.

README notes regex \p{...} as unsupported (separate from this).

doc/grammar.ebnf

@@ -122,6 +122,10 @@ unquote         = "~"  , form ;        (* (unquote form)          *)
 deref           = "@"  , form ;        (* (deref form)            *)
 metadata        = "^"  , meta-form , ws , form ;   (* attach metadata to form *)
 meta-form       = map | keyword | symbol | string ;
+(* Normalized like Clojure: a symbol or string is a type hint -> {:tag ...};
+   a keyword -> {keyword true}; a map is used as-is. On a symbol the metadata
+   rides on the symbol (it stays a bare symbol, so a hint like ^String is
+   transparent in params/lets/bodies); other targets use a runtime with-meta. *)
 
 (* --------------------------------------------------------------------------
    Dispatch forms — introduced by "#".