Readd removed constructor of Archive.

Pr #860 removed the constructor from (fd, offset, size).
This is a API break and we don't want that.

include/zim/archive.h

@@ -106,6 +106,23 @@ namespace zim
        */
       explicit Archive(int fd);
 
+      /** Archive constructor.
+       *
+       *  Construct an archive from a descriptor of a file with an embedded ZIM
+       *  archive inside.
+       *  Fd is used only at Archive creation.
+       *  Ownership of the fd is not taken and it must be closed by caller.
+       *
+       *  Note: This function is not available under Windows.
+       *
+       *  @param fd The descriptor of a seekable file with a continuous segment
+       *  representing a complete ZIM archive.
+       *  @param offset The offset of the ZIM archive relative to the beginning
+       *  of the file (rather than the current position associated with fd).
+       *  @param size The size of the ZIM archive.
+       */
+       Archive(int fd, offset_type offset, size_type size);
+
       /** Archive constructor.
        *
        *  Construct an archive from a descriptor of a file with an embedded ZIM

src/archive.cpp

@@ -45,6 +45,10 @@ namespace zim
     : m_impl(new FileImpl(fd))
     { }
 
+  Archive::Archive(int fd, offset_type offset, size_type size)
+    : Archive(FdInput(fd, offset, size))
+  {}
+
   Archive::Archive(const std::vector<FdInput>& fds)
     : m_impl(new FileImpl(fds))
     { }