Add support in the SDK for composite commands.

The CLI doesn't support them yet. I don't know of a good way of doing it.
If you consturct the sub_commands using the parse method of the corresponding
classes, there would be extra 'can_notify' and 'label' keys inside them
which the API would ignore. Only the options given directly to the composite
commands are acted upon by the API.
Adding support for the DbTapQuery Command
Support notify option
Merge pull request #48 from guptavishal/db_tap_query_command

Adding support for the DbTapQuery Command
Adding a new type - sqlserver
Add support for macros in composite-commands
Merge pull request #46 from mindprince/composite-command

Add support in the SDK for composite commands.
Merge pull request #49 from guptavishal/sqlserver

Adding a new type in dbtaps - sqlserver
Fix bug introduced in 9335343 where wrong command_type was getting passed.
Specify command_type explicitly for DbTapQueryCommand. This is needed for CompositeCommand to work properly.