Clean up and Documentation (#347) [skip ci]

* cmd,misc: move misc binaries to cmd/
* docs: add docs and move examples/ there
* misc: remove unused misc/assets dir
* docs: add configuration.md
* update README with better structure

Updates: #334

cmd/misc/process-cmd-test/main.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"os/signal"
+	"syscall"
+	"time"
+)
+
+/*
+**
+Test how exec.Cmd.CommandContext behaves under certain conditions:*
+
+  - process is killed externally, what happens with cmd.Wait() *
+    ✔︎ it returns. catches crashes.*
+
+  - process ignores SIGTERM*
+    ✔︎ `kill()` is called after cmd.WaitDelay*
+
+  - this process exits, what happens with children (kill -9 <this process' pid>)*
+    x they stick around. have to be manually killed.*
+
+  - .WithTimeout()'s cancel is called *
+    ✔︎ process is killed after it ignores sigterm, cmd.Wait() catches it.*
+
+  - parent receives SIGINT/SIGTERM, what happens
+    ✔︎ waits for child process to exit, then exits gracefully.
+*/
+func main() {
+
+	// swap between these to use kill -9 <pid> on the cli to sim external crash
+	ctx, cancel := context.WithCancel(context.Background())
+	//ctx, cancel := context.WithTimeout(context.Background(), 1000*time.Millisecond)
+	defer cancel()
+
+	//cmd := exec.CommandContext(ctx, "sleep", "1")
+	cmd := exec.CommandContext(ctx,
+		"../../build/simple-responder_darwin_arm64",
+		//"-ignore-sig-term", /* so it doesn't exit on receiving SIGTERM, test cmd.WaitTimeout */
+	)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	// set a wait delay before signing sig kill
+	cmd.WaitDelay = 500 * time.Millisecond
+	cmd.Cancel = func() error {
+		fmt.Println("✔︎ Cancel() called, sending SIGTERM")
+		cmd.Process.Signal(syscall.SIGTERM)
+
+		//return nil
+
+		// this error is returned by cmd.Wait(), and can be used to
+		// single an error when the process couldn't be normally terminated
+		// but since a SIGTERM is sent, it's probably ok to return a nil
+		// as WaitDelay timing out will override the any error set here.
+		//
+		// test by enabling/disabling -ignore-sig-term on the process
+		// with -ignore-sig-term enabled, cmd.Wait() will have "signal: killed"
+		// without it, it will show the "new error from cancel"
+		return errors.New("error from cmd.Cancel()") // sets error returned by cmd.Wait()
+	}
+
+	if err := cmd.Start(); err != nil {
+		fmt.Println("Error starting process:", err)
+		return
+	}
+
+	// catch signals. Calls cancel() which will cause cmd.Wait() to return and
+	// this program to eventually exit gracefully.
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
+	go func() {
+		signal := <-sigChan
+		fmt.Printf("✔︎ Received signal: %d, Killing process... with cancel before exiting\n", signal)
+		cancel()
+	}()
+
+	fmt.Printf("✔︎ Parent Pid: %d, Process Pid: %d\n", os.Getpid(), cmd.Process.Pid)
+	fmt.Println("✔︎ Process started, cmd.Wait() ... ")
+	if err := cmd.Wait(); err != nil {
+		fmt.Println("✔︎ cmd.Wait returned, Error:", err)
+	} else {
+		fmt.Println("✔︎ cmd.Wait returned, Process exited on its own")
+	}
+	fmt.Println("✔︎ Child process exited, Done.")
+}