Add install to README

Vanity URL

Add AlreadyLower, crumb a few nanos

Remove bounds checks from suffix functions

Good for another 5%:
    benchmark                old ns/op     new ns/op     delta
    BenchmarkStemBytes-8     145           137           -5.52%
    BenchmarkStem-8          296           289           -2.36%

Speed up findRException, calcR1R2

Stem/StemString -> StemBytes/Stem

Add StemString

Update README.md

Remove old test files

Performance improvements

    benchmark           old ns/op     new ns/op     delta
    BenchmarkStem-8     1721          230           -86.64%

    benchmark           old allocs     new allocs     delta
    BenchmarkStem-8     0              0              +0.00%

    benchmark           old bytes     new bytes     delta
    BenchmarkStem-8     12            0             -100.00%

Import upstream

Initial