Enhanced popen_spawn and added tests

- Use just newline character for end of line
- Use shlex to split cmd args
- Improved non-blocking read to act more like ptyspawn
- Fix send method and add sendline
- Add kill method
- Add several tests
Add test file
Merge pull request #1 from blink1073/pr/146

Enhancements to Popen_Spawn and added test