v0.11.1 Better handling of no-candidates and orphan candidates

What's new

• New codes.go with matcher code constants. Currently they are:
  900 - OK,
  901 - no candidates,
  902 - orphan observation
• Updated matcher enginge to preserve unmatched observations in results
• Do not call Viterbi on single point. Just use 2 * emission for probablity

For more info see PR: #39