Implement Multi-Process Handling (#7)

Refactor code to support starting of multiple back end llama.cpp servers. This functionality is exposed as `profiles` to create a simple configuration format. 

Changes: 

* refactor proxy tests to get ready for multi-process support
* update proxy/ProxyManager to support multiple processes (#7)
* Add support for Groups in configuration
* improve handling of Model alias configs
* implement multi-model swapping
* improve code clarity for swapModel
* improve docs, rename groups to profiles in config

proxy/process.go

@@ -113,7 +113,7 @@ func (p *Process) Stop() {
 	p.Lock()
 	defer p.Unlock()
 
-	if !p.isRunning {
+	if !p.isRunning || p.cmd == nil || p.cmd.Process == nil {
 		return
 	}