Update README.md

fix g++ version on OSX
[skip ci]
Fix OSX linker warning issue
Put MemCheck and Submit to "after_script" section to ignore possible failures
Put LEANREPO variable in .travis.yml to check the blessed repository inside of travis-ci.

It prevents other users from running heavy tasks on travis and submitting results to cdash server.
Update .travis.osx.yml

Turn off 'MEMCHECK' for OSX build.
[skip ci]
Fix typo

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Improve application type mismatch errors. We also show the implicit arguments (not just their types)

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Improve elaborator error messages

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>