Add method to install go packages

Several go related tools can be used within emacs, such as:
gocode, godef, goimports, golint, goflymake, etc.

The el-get-go method lets the 'go get' command take care of
downloading and building such tools.  The main advantage is letting
go get take care of resolving dependecies and building the binary,
rather than wedging into the :build property.
Go language related recipes

- go-autocomplete: change to use :type go

- go-company: change to use :type go

- go-def: helper used in go-mode

- go-flymake: flymake checker for go

- go-imports: override go-mode's gofmt-command

- go-lint: linter for go
Merge pull request #1488 from dougm/go

Go language related recipes and package installer