Implement special ditto documentation handling

[WebFreak001]

Stores ditto documentation using their actual documentation and has a special ditto flag on the documentation strings.

This is not backwards compatible with any code relying on documentation being "ditto" instead of the actual documentation, otherwise it's backwards compatible.

[ghost]

Look reasonable, maybe try to see about the two comments.
Also current DCD output in non-extended mode won't be modified if i understand correctly ?

[WebFreak001]

current non-extended mode should not notably get modified.

The current code is compatible with current tests, but I'm further extending it to also test ditto scopes. where I already found an issue

I think before this implementation there might have been an issue if a ditto was used on a function with different name as the one you are trying to test, which should now work just as the D compiler.

[WebFreak001]

The current code passes with all the tests in DCD (also using the example from the D ddoc spec) with ditto scopes.

For adding it in DCD we need a new tagged version of this after this is merged.

[ghost]

I let you put the appropriated tag yourself.

[WebFreak001]

should I do just a tag or use the "draft a release" button?

[ghost]

just a tag is enough since this is a low level library people usually don't care about having a nice changelog.