mapped_file documentation is incomplete

[jm4R]

mapped_file documentation doesn't say:

1. if destructor closes file
2. how we should deal with IO errors (std::copy(file.data(), ...) can't throw, I guess?)

One should read source code to get that information:
https://stackoverflow.com/questions/26608264/what-exceptions-does-boost-mapped-file-source-throw
https://stackoverflow.com/questions/7342045/are-boost-mapped-files-raii