Item11267: default to an empty tidyrc

- i.e. don't use the developer's custom $HOME/.perltidyrc
- SMELL: this doesn't use an extension's TIDY file if present
- same error in BuildContrib
Item11267: use an empty perltidyrc

- i.e. don't use ~/.perltidyrc
- add support for a default repo in ~/.buildcontrib
- docu fixes to BuildContrib, mostly formatting issues