[lexical_cast] missing signature in doc

[Akira Takahashi <faithandbrave@…>]

http://www.boost.org/doc/libs/1_52_0/doc/html/boost_lexical_cast/synopsis.html#boost_lexical_cast.synopsis.lexical_cast

now lexical_cast.hpp's sigunature:

namespace boost
{
    class bad_lexical_cast;
    template<typename Target, typename Source>
      Target lexical_cast(const Source& arg);
}

But, Boost 1.52.0 has N characters version. should be:

namespace boost
{
    class bad_lexical_cast;
    template<typename Target, typename Source>
      Target lexical_cast(const Source& arg);
    template <typename Target>
      Target lexical_cast(const AnyCharacterType* chars, std::size_t count);
}

[Antony Polukhin]

(In [82220]) Add missing signature to doc (refs #7831)

[Antony Polukhin]

(In [82224]) Merge from trunk

• Fixes #7799 (optimizations with std::array were not used)
• Fixes #7831 (documentation update)