Multiline step arguments (table diffing)

[paoloambrosio]

Implement passing tables to a step as documented in the Diffing tables section.

https://github.com/aslakhellesoy/cucumber/blob/master/legacy_features/wire_protocol_table_diffing.feature

[paoloambrosio]

Table diffing is going to be tricky if requested to Cucumber through the wire protocol, since it would stop the normal execution of a test and resume it later after the server response. I believe it is going to be much easier to implement table diffing in C++.

[paoloambrosio]

Reopen if we ever decide to do it.