Moved kernel exception formatting to kernel_exception_formatter.cpp.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Clean elaborator_exception pretty printing

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add proof by evaluation examples

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix pretty printer for evaluator

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix typo
Update .travis files to have consistent site/build names
Fix .travis files

- OSX sed expects parameter for "-i" option
- for Windows and OSX build, we need to get the commit hash of HEAD~
  instead of HEAD because we made an extra commit to trigger the build