added possibility to save fetched file into different name

Sometimes when you're getting the file from the website the filename doesn't match the PKG_NAME schema, this patch allows you to add the correct filename in the PKG_URL after the pipe char.

Without pipe char delimiter fetching works like before.

E.g.:
Setting: `PKG_URL="http://some.url/and/path/to/file|${PKG_NAME}-${PKG_VERSION}.tar.gz"`

Will save the contents of the `http://some.url/and/path/to/file` to file named `${PKG_NAME}-${PKG_VERSION}.tar.gz"`