Add comments to parser.cpp

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add is_prefix_of for hierarchical names

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add support for pretty printing Dags. Find unused prefix for naming shared expressions.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add syntax sugar for forall/exists expressions. Fix problem when pretty printing nested equalities.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Pretty print forall/exists expressions

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix interval::sin to suppress a warning
Update .travis.osx.yml to use precompiled gcc/mpfr/gmp, and copy precompiled lean binaries to dropbox