Update .travis.yml and .travis.osx.yml
On Linux:
 - push to the repo on bitbucket, to trigger email-diff
 - push to the lean-osx repo on github, to trigger osx build & test
 - run test coverage and upload to dropbox
 - run doxygen and upload to dropbox
 - upload compiled binaries to dropbox
 - secure passwords by putting "-q" option to git operations

On OSX:
 - build & test
 - upload compiled binaries to dropbox
 - roll back to HPC g++-4.9.0 + gmp & mpfr (homebrew)
 - patch the problem in <cstddef>, saved in dropbox
Implement dependencies on interval functions (exp, log, and trigonometric functions)
Add test normalizer interrupt

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add minor improvement to pretty printer

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Allow square brackets to be used in operator names

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add Echo command. Allow '\' 'n' escape sequence in strings.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add output_channel and state abstractions

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add methods for setting options. Add string output channel.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix cyclic reference: frontend -> state -> pp_formatter -> frontend. Now pp_formatter is only valid while frontend is still alive. This should not be problem in practice.

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