New output format in 0.6.0 stopped distinguishing warnings from errors

[Ben Stoutenburgh]

All warnings now show as E in the output.

```
ben@warden816:~/repos/bashate (master u=)$ bashate bashate/tests/samples/E042_bad.sh
bashate/tests/samples/E042_bad.sh:2:1: E042 local declaration hides errors
bashate/tests/samples/E042_bad.sh:6:1: E042 local declaration hides errors
bashate/tests/samples/E042_bad.sh:10:1: E042 local declaration hides errors
bashate/tests/samples/E042_bad.sh:11:1: E042 local declaration hides errors
4 bashate warning(s) found
```

At a tired glance, looks like logic for picking W or E is assigned to the 'warn' key but not used in the print statement in log_error().

[Ben Stoutenburgh (maristgeek)]

For clarifcation, prior to 0.6.0 warnings (whether from the message's default, or through the --warn option) would show up with a [W]. Looks like intention was to change error codes to be Wxxx or Exxx going forward.

```
ben@warden816:~/repos/bashate (master u=)$ bashate bashate/tests/samples/E042_bad.sh
[W] E042: local declaration hides errors: ' local foo=$(ls)'
 - bashate/tests/samples/E042_bad.sh : L2
[W] E042: local declaration hides errors: ' local foo=`ls`'
 - bashate/tests/samples/E042_bad.sh : L6
[W] E042: local declaration hides errors: ' local foo="$(ls)"'
 - bashate/tests/samples/E042_bad.sh : L10
[W] E042: local declaration hides errors: ' local bar="`ls`"'
 - bashate/tests/samples/E042_bad.sh : L11
4 bashate warning(s) found
```