Rework man generator with new go install format

With previous version, `go install` automatically picks up
package `man` and installs `gen.go` as `main` to the $GOPATH/bin which
is not what is expected. Move man page generator to separate
private folder.

man/Makefile

@@ -5,6 +5,6 @@ prepare:
 	gem specific_install -l smira/ronn
 
 generate:
-	go run gen.go
+	go run ../_man/gen.go
 
 .PHONY: prepare generate

man/gen.go

@@ -1,111 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"io/ioutil"
-	"log"
-	"os"
-	"os/exec"
-	"path/filepath"
-	"runtime"
-	"strings"
-	"text/template"
-
-	"github.com/smira/aptly/cmd"
-	"github.com/smira/commander"
-	"github.com/smira/flag"
-)
-
-func allFlags(flags *flag.FlagSet) []*flag.Flag {
-	result := []*flag.Flag{}
-	flags.VisitAll(func(f *flag.Flag) {
-		result = append(result, f)
-	})
-	return result
-}
-
-func findCommand(cmd *commander.Command, name string) (*commander.Command, error) {
-	for _, c := range cmd.Subcommands {
-		if c.Name() == name {
-			return c, nil
-		}
-	}
-
-	return nil, fmt.Errorf("command %s not found", name)
-}
-
-func capitalize(s string) string {
-	parts := strings.Split(s, " ")
-	for i, part := range parts {
-		if part[0] != '<' && part[0] != '[' && part[len(part)-1] != '>' && part[len(part)-1] != ']' {
-			parts[i] = "`" + part + "`"
-		}
-	}
-
-	return strings.Join(parts, " ")
-}
-
-var authorsS string
-
-func authors() string {
-	return authorsS
-}
-
-func main() {
-	command := cmd.RootCommand()
-	command.UsageLine = "aptly"
-	command.Dispatch(nil)
-
-	_, _File, _, _ := runtime.Caller(0)
-	_File, _ = filepath.Abs(_File)
-
-	templ := template.New("man").Funcs(template.FuncMap{
-		"allFlags":    allFlags,
-		"findCommand": findCommand,
-		"toUpper":     strings.ToUpper,
-		"capitalize":  capitalize,
-		"authors":     authors,
-	})
-	template.Must(templ.ParseFiles(filepath.Join(filepath.Dir(_File), "aptly.1.ronn.tmpl")))
-
-	authorsF, err := os.Open(filepath.Join(filepath.Dir(_File), "..", "AUTHORS"))
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	authorsB, err := ioutil.ReadAll(authorsF)
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	authorsF.Close()
-
-	authorsS = string(authorsB)
-
-	output, err := os.Create(filepath.Join(filepath.Dir(_File), "aptly.1.ronn"))
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	err = templ.ExecuteTemplate(output, "main", command)
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	output.Close()
-
-	out, err := exec.Command("ronn", filepath.Join(filepath.Dir(_File), "aptly.1.ronn")).CombinedOutput()
-	if err != nil {
-		os.Stdout.Write(out)
-		log.Fatal(err)
-	}
-
-	cmd := exec.Command("man", filepath.Join(filepath.Dir(_File), "aptly.1"))
-	cmd.Stdin = os.Stdin
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	err = cmd.Run()
-	if err != nil {
-		log.Fatal(err)
-	}
-}