v5.3.1

A bug fix release for map_view and set_view, which came with 5.3.0. Some of their read functions did not compile: visit(), cbegin(), cend() and locate(). Owning maps are unchanged, same hash values and same iteration order as 5.3.0.

• visit() on a view stored a const element in a non-const pointer. A view now passes value_type const& to the callback (#374, thanks @fhgffy!).
• cbegin() and cend() asked the value container for its cbegin(), which a view's container does not have, and neither does a read only value container you bring yourself. They now use the table's own const begin() and end() (#375).
• A new test calls every read function on a map_view, a set_view and on a table with its own read only value container, both mutable and const, so the next one of these fails in CI instead of in your build (#375, #376).

The inline namespace is v5_3_1.