added '-nosymlinks' parameter

...in order to restore windows compatibility (no 'ln -s ...' command)
fixed symlink inconsistency

...so that "nosymlinks" actually means "no symlinks at all".
The heuristic of detecting the OS is not needed then.
Reverted the import order to minimize difference from the upstream. Some changes to the explanation to -nosymlink link (it always works with -download).
Merge pull request #14 from ikedam/feature/12_nosymlinks

Some adjustment for #12