Include location handling for outline step.

This is needed by some formatters in cucumber, specifically the html formatter.
Add location to Ast::ExamplesTable::Header.

This is needed by the html formatter so that it can produce dom ids.
ExamplesTable::Row has location.

This is needed for the html formatter so that it can produce dom ids.
Merge pull request #24 from tom025/add-location-to-scenario-outline-step

Add location methods to some Ast nodes