Adds convention reason to conventions, useful for the living documentati...

[JakeGinnivan]

...on - fixed #37

[JakeGinnivan]

I think the why we have these conventions in place is useful. Especially when developers on teams hit a failing convention test for the first time.

Maybe errors should report the reason too, I only have added to the Html and Markdown reporters

[JakeGinnivan]

Rebased this one so it is able to be merged. This was an idea, I just implemented it while I was working on CT so if @kkozmic you like the idea you can just merge it

[kkozmic]

should it be on a IConvention though, or rather passed to the Convention.Is() method?

[JakeGinnivan]

I think it is more static than the title, so i think property is ok.

It also means when you create a custom convention, you get prompted to write the reason before implementing, which is good I think

[kkozmic]

So you think that would always be provided by the implementor of the convention, not the user? You think it would suffice to have one for all usages of the convention?

Does every convention require it though? If you have a convention that you put IValueConverters all in a single place... there's no elaborate reasons behind it - you just do it to keep things tidy... not sure if explanation is necessary...

[JakeGinnivan]

Exactly, it would always be provided by the implementor of the convention.

For some yes, the explanation is not groundbreaking, but it is useful for the living documentation. That Wiki scenario where project conventions are.

For example the Dto one is https://github.com/TestStack/ConventionTests/pull/46/files#L8R46