Name already in use

Fixes #507.

Fixes #506.

Fixes #505.

Returned value can be nil there and hence causes panic.

Also add new command "gocode options" which prints config options in an
extended form (unlike "gocode set").

This makes gocode pass go vet ./...

Fixes #484.

#479

Fixes #469.

Emacs-company plugin is switched to "csv-with-package" format.
Adding one field to "csv" formatter breaks local sublime plugin. It's python
there, args spread goes into a function with 3 arguments, it says you give it
4 and throws an exception.
Fucking fuck. I said - backwards compatibility, please.
See: #463

Pass through package names, use it for godoc in emacs-company

* Add the -u flag (customizably) to the `go doc` command line: This
  ensures that un-exported/private names get matched & have their docs
  displayed, too.
* Add a company-go customization option for the `go doc` command line.
* Make sure that if company-go gets no package, it looks in the
  current directory. This can more reliably show documentation for the
  current package's names (including internals).

There were some places that could have been nil, and the pcache might
just not contain an entry either. This change should guard against
these cases & use a default (no package) instead.

Using the package information the 4th field in CSV output,
call `godoc` on the symbol being completed. This activates the
automatic documentation functionality for go in company.

This makes JSON and CSV formatters emit the import path for the
package defining the symbol being completed. This should help tools
like company get documentation for symbols, as gocode expects
`importpath.symbol` as input.

This should let us retain each package's import path, potentially
useful for attaching to the symbols we emit (definitely useful for
gocode further down the line).

When you import a package "x", and do autocompletions which involve types from
"x", for ages gocode is adding default type alias of "x" to the types when
printing them out. This is purely for improving readability, because types
within a scope of the package are local, however they are not local to you,
usually. But there is a case when you import a package and redefine its name
via aliased import statement. E.g.
    import myio "io"
Yet, gocode didn't respect that and used default alias anyway. Sadly some
people use very ugly default aliases like "v1" (stands for version 1). To
overcome this problem a hack is added. It doesn't work in all cases, but it
works in some cases. When you import package with a custom alias for a current
file. Gocode will try to use that alias for package's own types, when you talk
to them directly via that package (e.g. accessing them directly or indirectly
via your package alias). E.g.
    package main
    import myast "go/ast"
    func main() {
        myast.NewPack#
    }
Will show myast.NewPackage function signature where types are prefix with
"myast.". However if you do something like that:
    import myio "io"
    import "compress/bzip2"
    ...
    bzip2.NewR#
bzip.NewReader function will use default "io" alias which is "io". Maybe I'll
improve the hack later to include this case as well.

Emacs package go-autocomplete.el:
Add option to let users specify the path (and/or name)
of the gocode binary