whitespace: be more like other Ruby code
remove whitespace at end of lines

(My editor does this)
add support for mangle table

There are no tests. (The existing did not have any.)

This commit is largely borrowed from:

https://github.com/rtkmhart/cookbook-simple-iptables/commit/b09d31c46ebabcdf424356f9d4e877150e5745a1
Merge pull request #1 from bluemont/mangle

Add mangle table support