Change places adding '-' to testname output.

The '-' included in testname output was added at _bshtap_test_ok_ng,
but some features(e.g. skip) require to suppress '-' from their output.
This commit moves the places adding '-' to the output from
_bshtap_test_ok_ng to _bshtap_test_ok/_bshtap_test_ng.

It is to prepare adding 'skip' feature.
Add a wrapper function for cmp_ok
Add new feature 'skip'
Add documentation about skip
Add a new feature todo
Add documentation about todo
Merge branch 'skip-and-todo'

* skip-and-todo:
  Add documentation about todo
  Add a new feature todo
  Add documentation about skip
  Add new feature 'skip'
  Add a wrapper function for cmp_ok
  Change places adding '-' to testname output.
Drop 'echo -n' #2

Drop echo -n for MacOS X.  All echo cannot be removed because
'echo "$@"' is little hard to be replaced by 'printf'.
So I decided to remove only 'echo -n' from my code for now.
Update Readme
Merge branch 'drop-echo-p2'

* drop-echo-p2:
  Drop 'echo -n' #2