Project refactor, add anthropic API support

- Split pkg/cli/cmd.go into new pkg/cmd package
- Split pkg/cli/functions.go into pkg/lmcli/tools package
- Refactor pkg/cli/openai.go to pkg/lmcli/provider/openai

Other changes:

- Made models configurable
- Slight config reorganization

main.go

@@ -1,15 +1,18 @@
 package main
 
 import (
-	"fmt"
-	"os"
-
-	"git.mlow.ca/mlow/lmcli/pkg/cli"
+	"git.mlow.ca/mlow/lmcli/pkg/lmcli"
+	"git.mlow.ca/mlow/lmcli/pkg/cmd"
 )
 
 func main() {
-	if err := cli.Execute(); err != nil {
-		fmt.Fprintln(os.Stderr, err.Error())
-		os.Exit(1)
+	ctx, err := lmcli.NewContext()
+	if err != nil {
+		lmcli.Fatal("%v\n", err)
+	}
+
+	root := cmd.RootCmd(ctx)
+	if err := root.Execute(); err != nil {
+		lmcli.Fatal("%v\n", err)
 	}
 }