Added configurable netrc path

Nice work!

Netrc was not working on windows as the default paths en env variables differ. 
I extended the --netrc with configurable path. If no path is given or -n, -c and -u are omitted
a default netrc path is tried ($HOME/.netrc on \*nix\* or
%USERPROFILE%\\_netrc on windows).

The -n -c and -u options ar no longer required. If no option is given the default netrc path is tried by default. Order of preference is -c, -u, -n.