bin/gochainimports: new command
bin/gochainimports: new command

This command is a wrapper for goimports, adding the flag
'-local chain/'. This flag will instruct goimports to
treat import paths with prefix 'chain/' differently,
adding them in a separate group after standard library
packages and 3rd-party packages.

To use this, first update goimports:

    go get -u golang.org/x/tools/cmd/goimports

Then, configure your editor to run 'gochainimports' rather
than 'goimports' as its formatting command. For example, in
vim, you would add the following line to the file
$HOME/.vim/ftplugin/go.vim.

    let g:go_goimports_bin = "gochainimports"


Closes chain/chainprv#1137.
Reviewers: da39a3ee5e6b4b0d3255bfef95601890afd80709@jbowens




chain/chain,chain/chain,chain/chain,chain/chain,chain/chain,chain/chain