Big refactoring

[krlmlr]

• Explicit ctx in all tester functions
• Move tester functions to separate modules
  • At least one module per method tested, not one module per class
  • Find a better home for utility functions
• Prepare tests so that prose can be embedded easily
• Support an easy way to run individual test functions
• Sane ordering of methods (like in DBI vignette)
• How to document/test interplay between methods?
  • Fetch results
  • Transaction
  • Parameters
  • ...

[krlmlr]

Closing this. There will be a more or less 1:1 mapping from DBI functions to specifications+tests.