more lenient return contract for `select-from-metas` (fixes #184)

pollen/core.rkt

@@ -62,7 +62,7 @@
 (define+provide/contract (select-from-metas key metas-source [caller 'select-from-metas])
   ;; output contract is a single txexpr-element
   ;; because metas is a hash, and a hash has only one value for a key.
-  ((coerce/symbol? (or/c is-meta-value? pagenode? pathish?)) (symbol?) . ->* . (or/c #f txexpr-element?))
+  ((coerce/symbol? (or/c is-meta-value? pagenode? pathish?)) (symbol?) . ->* . any/c)
   (hash-ref (match metas-source
               [(? is-meta-value? ms) ms]
               [_  (get-metas metas-source caller)]) key #false))

pollen/private/ts.rktd

@@ -1 +1 @@
-1542912991
+1542913104

pollen/scribblings/core.scrbl

@@ -145,7 +145,7 @@ Note that if @racket[_doc-source] is a relative path or pagenode, it is treated
 (select-from-metas
 [key symbolish?]
 [meta-source (or/c hash? pagenodeish? pathish?)])
-(or/c #f xexpr?)]
+any/c]
 Look up the value of @racket[_key] in @racket[_meta-source]. The @racket[_meta-source] argument can be either 1) a hashtable representing @racket[metas] or 2) a pagenode or source path that identifies a source file that provides @racket[metas]. If no value exists for @racket[_key], you get @racket[#f]. 
 
 Note that if @racket[_meta-source] is a relative path or pagenode, it is treated as being relative to @racket[current-project-root]. If that's not what you want, you'll need to convert it explicitly to a complete-path (e.g., with @racket[path->complete-path] or @racket[->complete-path]).