Move Dsymbol::emitDitto into a free function
Move ScopeDsymbol::emitMemberComments to a free function
Move Dsymbol::toDocBuffer into a visitor class
Move Dsymbol::emitComment into a visitor class
Move Module::gendocfile into a free function
Merge pull request #3288 from yebblies/doc

[DDMD] [refactor] Move Module::gendocfile and related functions into free functions