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/sqlmesh.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:        "sqlmesh",
 		Description: "SQLMesh command line tool",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "init", Description: "Create a new SQLMesh repository"},
 			{Name: "render", Description: "Render a model's query, optionally expanding referenced models"},
 			{Name: "evaluate", Description: "Evaluate a model and return a dataframe with a default limit of 1000"},
@@ -26,7 +26,7 @@ func init() {
 			{Name: "rollback", Description: "Rollback SQLMesh to the previous migration"},
 			{Name: "create_external_models", Description: "Create a schema file containing external model schemas"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--paths", Description: "Paths to SQLMesh project files"},
 			{Name: "--config", Description: "Path to config file"},
 			{Name: "--gateway", Description: "The name of the gateway"},