refactor(commands): separate commands and its core into two folders (#32)

- I think it would be better if one for commands only, one for the spec
handling core logic so people won't be confused by the core logic inside
the commands folder (cleaner I guess)
- Regen docs

commands/python/sqlfluff.go

@@ -1,14 +1,14 @@
 package python
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "sqlfluff",
 		Description: "A dialect-flexible and configurable SQL linter",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "lint", Description: "Lint SQL files via passing a list of files or using stdin"},
 			{Name: "templater", Description: "Name of templater to use, eg. raw"},
 			{Name: "dialect", Description: "Name of dialect, eg. ANSI"},
@@ -20,7 +20,7 @@ func init() {
 			{Name: "version", Description: "Show the version of sqlfluff"},
 			{Name: "rules", Description: "Show the current rules in use"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--version", Description: "Show the version and exit"},
 			{Name: "--help", Description: "Show help for sqlfluff"},
 			{Name: "--nocolor", Description: "No color - output will be without ANSI color codes"},