Allow --dl to be relative to _SCRIPTDIR_

docs/exec.md

@@ -75,6 +75,16 @@ first line accordingly:
 echo "Hello world\n";
 ```
 
+The `--dl` can be relative. By default, it's relative to the CWD (which is
+more intuitive for direct invocations), but you may make it relative to the
+script with the constant `_SCRIPTDIR_`.
+
+```bash
+#!/usr/bin/env pogo --dl='_SCRIPTDIR_/.my-script.deps'
+<?php
+echo "Hello world\n";
+```
+
 Or if you wanted to lock deps into a read-only mode for multiuser systems:
 
 ```php

src/Command/DownloadCommandTrait.php

@@ -1,6 +1,7 @@
 <?php
 namespace Pogo\Command;
 
+use Pogo\PathUtil;
 use Pogo\PogoProject;
 use Symfony\Component\Console\Input\InputInterface;
 
@@ -48,9 +49,10 @@ public function initProject(InputInterface $input, $target) {
    * @return string
    */
   public function pickBaseDir(InputInterface $input, $scriptMetadata) {
-    $result = $input->getOption('dl');
-    if ($result) {
-      return $result;
+    $dl = $input->getOption('dl');
+    if ($dl) {
+      $dl = preg_replace('/^_SCRIPTDIR_/', dirname($scriptMetadata->file), $dl);
+      return PathUtil::evaluateDots(PathUtil::makeAbsolute($dl));
     }
 
     // Pick a base and calculate a hint/digested name.

src/Command/HelpCommand.php

@@ -43,6 +43,7 @@ protected function execute(InputInterface $input, OutputInterface $output) {
     $output->writeln("<comment>Action-Options:</comment>");
     $output->writeln("  <info>-f</info>          Force; recreate project, even if it appears current");
     $output->writeln("  <info>--dl=DIR</info>    Output dependencies in this directory");
+    $output->writeln("              Use constant _SCRIPTDIR_ to start relative to the target script.");
     $output->writeln("");
     $output->writeln("<comment>Environment:</comment>");
     $output->writeln("  <info>POGO_BASE</info>   Default location for output folders");