Implement unix::ftruncate correctly in Visual C++

Visual C++ does not provide ftruncate64 as MingW so to support 64 bit
sizes use Windows API directly.
Other differences between Visual C++ and MingW versions

Backport my changes to make Visual C++ compile to MingW code.
Remove a warning giving a warning

Block number was truncate to 32 bytes on some platforms (like Windows and
Linux 32).
Add readme for Windows
Update files after the small "release"

Remove old boost file and update web page.
No official release, only a development improvement.