Gometalinter integration

[fatih]

This PR adds a new command called :GoMetaLinter which uses the gometalinter tool. Because gometalinter invokes other tools to gather the final output some of can be canceled on big source code calls. This can be of course changed with flags passed to gometalinter. I've decided to limit it and make it a little bit more usable for Vim. So our command :GoMetaLinter is a little bit restricted, but with option to totally change the behavior how it would work.

For now we have the following settings:

let g:go_metalinter_command = ""
let g:go_metalinter_enabled = ['vet', 'golint']
let g:go_metalinter_path = "./..."

This causes the following command to be generated and executed:

gometalinter --disable-all --enable=vet --enable=golint ./...

To add/remove linters just change it for your own needs:

let g:go_metalinter_enabled = ['vet', 'golint', 'deadcode', 'errcheck']

However, if the user change the g:go_metalinter_command command to something different, vim-go will call the command without modifying anything. Example (which basically calls all default linters specified by gometalinter):

let g:go_metalinter_command = "gometalinter ./..."

Right now this is how it looks like and everything seems to work perfect:

We also have a mapping to invoke it easily. For example the following calls :GoMetaLinter with the shortcut bound to <Leader>l:

au FileType go nmap <Leader>l <Plug>(go-metalinter)

Todos:

• Add :GoMetaLinter command
• Specify the list of linters explicitly with g:go_metalinter_enabled
• Override the generated command if the user wants to control with itself with g:go_metalinter_command
• Pass directory as argument to :GoMetaLinter
• Add documentation and update readme
• Add mapping so we can easily invoke it

Fixes #320

[fatih]

This is now finished, will be a part of our upcoming release.