implement new 'zrepl status'

Primary goals:

- Scrollable output ( fixes #245 )
- Sending job signals from status view
- Filtering of output by filesystem

Implementation:

- original TUI framework: github.com/rivo/tview
- but: tview is quasi-unmaintained, didn't support some features
- => use fork https://gitlab.com/tslocum/cview
- however, don't buy into either too much to avoid lock-in

- instead: **port over the existing status UI drawing code
  and adjust it to produce strings instead of directly
  drawing into the termbox buffer**

Co-authored-by: Calistoc <calistoc@protonmail.com>
Co-authored-by: InsanePrawn <insane.prawny@gmail.com>

fixes #245
fixes #220

util/choices/choices.go

@@ -0,0 +1,98 @@
+// Package choice implements a flag.Value type that accepts a set of choices.
+//
+// See test cases or grep the code base for usage hints.
+package choices
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+)
+
+type Choices struct {
+	choices    map[string]interface{}
+	typeString string
+	value      interface{}
+}
+
+var _ flag.Value = (*Choices)(nil)
+
+func new(pairs ...interface{}) Choices {
+	if (len(pairs) % 2) != 0 {
+		panic("must provide a sequence of key value pairs")
+	}
+	c := Choices{
+		choices: make(map[string]interface{}, len(pairs)/2),
+		value:   nil,
+	}
+	for i := 0; i < len(pairs); {
+		key, ok := pairs[i].(string)
+		if !ok {
+			panic(fmt.Sprintf("argument %d is %T but should be a string, value: %#v", i, pairs[i], pairs[i]))
+		}
+		c.choices[key] = pairs[i+1]
+		i += 2
+	}
+	c.typeString = strings.Join(c.choicesList(true), ",") // overrideable by setter
+	return c
+}
+
+func (c *Choices) Init(pairs ...interface{}) {
+	*c = new(pairs...)
+}
+
+func (c Choices) choicesList(escaped bool) []string {
+	keys := make([]string, len(c.choices))
+	i := 0
+	for k := range c.choices {
+		e := k
+		if escaped {
+			e = fmt.Sprintf("%q", k)
+		}
+		keys[i] = e
+		i += 1
+	}
+	return keys
+}
+
+func (c Choices) Usage() string {
+	return fmt.Sprintf("one of %s", strings.Join(c.choicesList(true), ","))
+}
+
+func (c Choices) InputForChoice(v interface{}) (string, error) {
+	for input, choice := range c.choices {
+		if choice == v {
+			return input, nil
+		}
+	}
+	return "", fmt.Errorf("choice not registered at .Init(): %v", v)
+}
+
+func (c *Choices) SetDefaultValue(v interface{}) {
+	c.value = v
+}
+
+func (c Choices) Value() interface{} {
+	return c.value
+}
+
+func (c *Choices) Set(input string) error {
+	v, ok := c.choices[input]
+	if !ok {
+		return fmt.Errorf("invalid value %q: must be one of %s", input, c.Usage())
+	}
+	c.value = v
+	return nil
+}
+
+func (c *Choices) String() string {
+	return "" // c.value.(fmt.Stringer).String()
+}
+
+func (c *Choices) SetTypeString(ts string) {
+	c.typeString = ts
+}
+
+func (c *Choices) Type() string {
+	return c.typeString
+}