remove decode() on show-options output due to UnicodeDecodeError

This exception may happen when tmux.conf contains non-ascii chars,
such as in the case of status-line formatting is configured by
powerline with unicode chars or other tmux theming utils.
Use correct window base index to switch to first window
Disable setting of status left-width to length of session name
Explicitly decode show-options output with utf-8
Set status-left-length to session_name length only if already shorter
Merge pull request #5 from vuduchild/master

UnicodeDecodeError on tmux.conf parsing, incorrect windows base index used for switching to first window on session creation