CharSequence methods need testing, Java 8 enhancements

[headius]

I am fixing ByteList to properly honor the contract of CharSequence by considering encoded character offsets and lengths. There are a few outstanding to-do's:

• Better testing. I did not add tests for this. Tests should cover ASCII, ASCII-compatible, fixed width, and variable width encodings. Tests should include offsets at or outside begin/realSize to ensure edge characters work right and invalid offsets produce proper error values (and exceptions where appropriate).
• Java 8 enhancements for streams. ByteList could more efficiently support Java 8 streams by providing its own stream implementation that understands the current byte offsets. This may not be possible to support without requiring Java 8.

[headius]

See also #9 which is related to this work. cc @eregon.