Implement major enhancements to plugin manager (v1.2.0 & v1.3.0)

This commit introduces significant improvements and new features to the plugin manager:

- Add plugin discovery system and remote repository support
- Implement plugin update system with digital signature verification
- Enhance plugin lifecycle hooks (PreLoad, PostLoad, PreUnload)
- Improve dependency management with custom version comparison
- Introduce lazy loading for optimized plugin performance
- Implement comprehensive error handling and logging
- Enhance concurrency safety with fine-grained locking
- Add plugin statistics tracking
- Remove external version comparison dependencies
- Improve hot-reload functionality with graceful shutdown
- Add SSH key support for remote repositories
- Implement Redbean server integration for plugin repositories

This update significantly improves the plugin manager's functionality,
security, and performance, providing a more robust and flexible system
for managing plugins in Go applications.

examples/main.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+    "fmt"
+    "log"
+    "path/filepath"
+
+    pm "github.com/matt-dunleavy/plugin-manager"
+)
+
+func main() {
+    // Initialize the plugin manager
+    manager, err := pm.NewManager("plugins.json", "./plugins", "public_key.pem")
+    if err != nil {
+        log.Fatalf("Failed to create plugin manager: %v", err)
+    }
+
+    // Subscribe to plugin events
+    manager.SubscribeToEvent("PluginLoaded", func(e pm.Event) {
+        fmt.Printf("Plugin loaded: %s\n", e.(pm.PluginLoadedEvent).PluginName)
+    })
+
+    // Load plugins
+    plugins := []string{"hello.so", "math.so"}
+    for _, plugin := range plugins {
+        err := manager.LoadPlugin(filepath.Join("./plugins", plugin))
+        if err != nil {
+            log.Printf("Failed to load plugin %s: %v", plugin, err)
+        }
+    }
+
+    // List loaded plugins
+    loadedPlugins := manager.ListPlugins()
+    fmt.Println("Loaded plugins:", loadedPlugins)
+
+    // Execute plugins
+    for _, name := range loadedPlugins {
+        err := manager.ExecutePlugin(name)
+        if err != nil {
+            log.Printf("Failed to execute plugin %s: %v", name, err)
+        }
+    }
+
+    // Get and print plugin stats
+    for _, name := range loadedPlugins {
+        stats, err := manager.GetPluginStats(name)
+        if err != nil {
+            log.Printf("Failed to get stats for plugin %s: %v", name, err)
+        } else {
+            fmt.Printf("Stats for %s: Executions: %d, Last execution time: %v\n",
+                name, stats.ExecutionCount, stats.LastExecutionTime)
+        }
+    }
+
+    // Unload a plugin
+    err = manager.UnloadPlugin("hello.so")
+    if err != nil {
+        log.Printf("Failed to unload plugin: %v", err)
+    }
+
+    fmt.Println("Remaining plugins:", manager.ListPlugins())
+}