support `ghq import` subcommand
doc
prefix command with bang
Add --all option to the root command
Include zsh completion into release files
Add 'root' subcommand completion
Merge pull request #40 from aaa707/add_root_command

Add --all option to the root command
Merge pull request #41 from itiut/include-zsh-completion-into-releases

Include zsh completion into release zip files
Merge pull request #42 from syohex/update-subcommands

Add 'root' subcommand completion
fixup docs and zsh completion
Merge remote-tracking branch 'origin/import-subcommand'

Closes #38

Conflicts:
	commands.go
Merge pull request #44 from motemen/zsh-completion-import

fixup docs and zsh completion
update docs
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