Remove "explicit" from Endian type constructors. Rationale: Having to write "cntr.insert(big_int32_t(value))" instead of "cntr.insert(value)" gets old fast when you are writing application code and the use case arises more or less continuously. Additionally, the use of an endian type is an implementation detail that should not leak into the application code that needs to create values of the type. Furthermore, the ambiguities that caused the constructors to be made explicit no longer occur; they were eliminated when BOOST_MINIMAL_INTEGER_COVER_OPERATORS was introduced to removed a dependency on boost/operators.hpp. If an ambiguity does arise, it is easy to clear via a static_cast or a function-style cast.