Preparing for promise based engine
Versioned packages.

Each package now has a SxVersion constant. It is set to the Hex SHA1 of
all the sources files in the package. SxVersion allows sx to know when a
package changed and, as a result, which aggregates need to be
recalculated.

TODO:
- The transformations need to use SxVersion.
First import
First import
Removed lang (preparing for sx-lang-master merge)
Subtree merged in lang/
added missing sx_step_names
Subtree merged in lang/
Use the BOXEN_REDIS_PORT when present
Fixed sxdoc
Merge branch 'sx-lang-master' into fd-structured-change-descriptions
Include .sx files
Merge branch 'sx-lang-master' into fd-structured-change-descriptions
Updated the example
Added some experimental templates
Merge branch 'fd-structured-change-descriptions'