Fix misc issues

[fogti]

This pull request should address all issues found via lints (clippy), fix some formatting and inconsistency issues.

Changes

• lib.rs
  • use dyn in TStream declaration
  • use write_all when appropriate (needs testing)
  • some cases of write/write_all should probably be replaced with error handling of std::io::ErrorKind::Interrupted
• byte.rs, negotiation.rs: all files should use unix line endings
• (optional, bors.toml): prepare bors-ng usage to improve handling of parallel pull requests (currently, we got lucky most of the time and didn't need intervention...)

Travis builds

• issues found @ https://travis-ci.org/SLMT/telnet-rs/jobs/561074704
• last travis run with working clippy: https://travis-ci.org/zserik/telnet-rs/jobs/561405997
• I pinned a rustc nightly with a working clippy.