Update textproc/LDoc to version 1.4.6.

Prompted by https://repology.org.

Changes since 1.4.5:
-  typo in last commit (Eagle eyes of Gary)
-  issue #251 avoid potential clash between built-in and custom defined
    kinds like sections
-  Issue #248 overeager error messages for module-level fields
-  Issue #248: assignment wrong way around (Monday morning mode)
-  Issue #248 standalone field considered a parse error; reset is_local
    after parse_error set

(alnsn)