Various go parser improvements

Here are some go parser improvements and a torture unit test. At the end I gave up the idea of more detailed struct and interface parsing (at least for now) because it would require a bit more time to do it right. I went through the parser and it seems quite good overall now.

Regarding the scope patch, I don't know - it makes sense for ctags but looks stupid in the Symbols view of Geany (which I actually don't use so I don't care that much). Maybe it's somehow fixable in Geany itself - I had a look at symbols.c but the tree code looks quite complicated and I didn't have the patience to study it more.