WIP - Rop experiment

#464 

Submitting to get some feedback. 
I've applied (at least tried to) Railway Oriented Programming to two commands: Convert from nuget and Simplify. The results / errors of a command are handled by call-site in PublicApi.
Pros
 - I find the code a bit easier to reason about 
 - No modification in file system is performed until the command returns success result

Cons
 - code overhead for the infrastructure
 - in order to fully benefit from the technique, probably all commands ought to be transformed to use it
(at ome point in the future) This module should be extracted into separate project and and included via github linking.