Add Go for benchmarks

I've implemented mixed case in Go.

## Results
### Golang

Memory Virt/Res: 47428/7640
```bash
$ cat "16 cores, go mixed_case.txt"
17.87
```

### Scala
Memory Virt/Res: 4644M/711M
```bash
$ cat "16 cores, scala mixed_case.txt"
41.18
```

### Erlang
Memory Virt/Res: 363M /179M
```bash
$ cat "16 cores, erlang mixed_case.txt"
52.98
```

## Setup
2 x Intel(R) Xeon(R) CPU           E5620  @ 2.40GHz