Add test data from snowball website

http://snowball.tartarus.org/algorithms/english/stemmer.html

When test-data/tartarus-voc-output.txt is the same as
reference/tartarus-voc-output-golden.txt, this library will be done.
Start a test input/output file convention

List of words is test-data/x.txt, expected output is
test-data/x-output.txt
Test against both input/output files we have

It's so fast we may as well check all these words!
cargo test suppresses output anyway so don't bother
Wheee mixing 2 spaces and 4 spaces!
Rename the binary to porter2
Rename travis and rust-ci projects to porter2
Bump version
Add more metadata to cargo file