create abstract method
Creates the directory with this name.
If recursive
is false, only the last directory in the path is
created. If recursive
is true, all non-existing path components
are created. If the directory already exists nothing is done.
Returns a `Future<Directory>`
that completes with this
directory once it has been created. If the directory cannot be
created the future completes with an exception.
Implementation
Future<Directory> create({bool recursive = false});