NewickIO: whitespace tweaks
NewickIO: parse confidence values less stringently.

Moved confidence parsing to a separate function. Don't require confidences to be
in [0.0, 1.0] and don't treat integer confidences as percentages (i.e. dividing
by 100). These choices are left in the comments for future consideration.
Merge branch 'master' of github.com:biopython/biopython