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>
Fix clang++ error

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