Simplified WARC Reader

Don't use Content-Length header to read content in.

Potential issues:
- It uses the "WARC/1.0" line stamp as a delimiter.  If a record has "\nWARC/1.0" in the response body somewhere, this could cause issues.  That seems like an outlandish outlier, though, in comparison with the grief we've had with Content-Length reads.
- Interface isn't as pretty.  Have to:
```python
from warc.warc import SimpleWARCReader
reader = SimpleWARCReader(open('path/to/file.warc', 'r'))
```
- Can't read gzipped files (but then the original library can't either, not really.)