concat_map inlining for BatStream and BatEnum

I have run some benchmarks with lilis, the result is ~1.4 time faster for BatStream and ~1.2 time faster for BatEnum.
The tests seem to pass (if `make test` is enough).
Are the tests for BatEnum.concat_map enough ? 
Should I add test for BatStream ? The file is quite deserted ...

Here are the benchs. BatSeq is here for reference.
Before : 
```
 --- Lsystem Von_koch for 7 iterations ---
           Rate         Stream     Enum      Seq
  Stream 2.42+-0.02/s       --     -80%     -94%
    Enum 12.0+- 0.4/s     395%       --     -68%
     Seq 37.3+- 0.2/s    1442%     211%       --

 --- Lsystem dragon for 15 iterations ---
           Rate         Stream     Enum      Seq
  Stream 1.40+-0.01/s       --     -84%     -94%
    Enum 8.56+-0.12/s     513%       --     -64%
     Seq 23.7+- 0.3/s    1596%     177%       --

 --- Lsystem Tetradragon for 12 iterations ---
            Rate          Stream     Enum      Seq
  Stream 0.209+-0.001/s       --     -79%     -94%
    Enum  1.02+- 0.02/s     386%       --     -69%
     Seq  3.27+- 0.01/s    1465%     222%       --
```

After 
```
 --- Lsystem Von_koch for 7 iterations ---
           Rate         Stream     Enum      Seq
  Stream 4.46+-0.02/s       --     -67%     -89%
    Enum 13.7+- 0.1/s     207%       --     -66%
     Seq 40.7+- 1.0/s     814%     198%       --

 --- Lsystem dragon for 15 iterations ---
           Rate         Stream     Enum      Seq
  Stream 2.80+-0.01/s       --     -73%     -89%
    Enum 10.3+- 0.1/s     267%       --     -61%
     Seq 26.4+- 0.1/s     844%     157%       --

 --- Lsystem Tetradragon for 12 iterations ---
            Rate          Stream     Enum      Seq
  Stream 0.364+-0.005/s       --     -70%     -90%
    Enum  1.20+- 0.01/s     229%       --     -66%
     Seq  3.51+- 0.01/s     863%     193%       --
```

P.S. : I just saw the benchsuite, Do I add something there ?