named arguments in vksprintf now allow dots

- fixed missing escape character (\) for the hyphen within the character
class of the second group
- added the dot character (.) to the allowed characters within the
  second group
added a formatter to generate plantext templates

the usecase that reasons this implementation is me wanting to have a file
with just one setting written to it in plain text.
concrete we are talking about a file called 'environment' which would
contain a string like 'development-foobar'.
listed 0.5.0 changes