Refactor cli (#329)

- move cli files from `cli/drone` to `cli/`
- move cli main to `cmd/cli/main.go` to match agent and server
- use version from `version/version.go` to match agent and server

cli/exec/line.go

@@ -0,0 +1,67 @@
+package exec
+
+import (
+	"fmt"
+	"os"
+	"strings"
+	"time"
+)
+
+// Identifies the type of line in the logs.
+const (
+	LineStdout int = iota
+	LineStderr
+	LineExitCode
+	LineMetadata
+	LineProgress
+)
+
+// Line is a line of console output.
+type Line struct {
+	Proc string `json:"proc,omitempty"`
+	Time int64  `json:"time,omitempty"`
+	Type int    `json:"type,omitempty"`
+	Pos  int    `json:"pos,omityempty"`
+	Out  string `json:"out,omitempty"`
+}
+
+// LineWriter sends logs to the client.
+type LineWriter struct {
+	name  string
+	num   int
+	now   time.Time
+	rep   *strings.Replacer
+	lines []*Line
+}
+
+// NewLineWriter returns a new line reader.
+func NewLineWriter(name string) *LineWriter {
+	w := new(LineWriter)
+	w.name = name
+	w.num = 0
+	w.now = time.Now().UTC()
+
+	return w
+}
+
+func (w *LineWriter) Write(p []byte) (n int, err error) {
+	out := string(p)
+	if w.rep != nil {
+		out = w.rep.Replace(out)
+	}
+
+	line := &Line{
+		Out:  out,
+		Proc: w.name,
+		Pos:  w.num,
+		Time: int64(time.Since(w.now).Seconds()),
+		Type: LineStdout,
+	}
+
+	fmt.Fprintf(os.Stderr, "[%s:L%d:%ds] %s", w.name, w.num, int64(time.Since(w.now).Seconds()), out)
+
+	w.num++
+
+	w.lines = append(w.lines, line)
+	return len(p), nil
+}