Fix relative require

Requiring from one file to another works, requiring one file that requires another doesn't. This change fixes that.

The problem was the execution context was being threaded through unchanged, instead it should have been modifying the source path to reflect that a different document was being executed.

Close #80

lib/rundoc/code_command/rundoc/require.rb

@@ -14,12 +14,17 @@ def to_md(env = {})
       end
 
       def call(env = {})
-        document_path = @path.expand_path(env[:context].source_dir)
+        execution_context = env[:context]
+        document_path = @path.expand_path(execution_context.source_dir)
 
-        puts "rundoc.require: Start executing #{@path.to_s.inspect}"
         output = Rundoc::Parser.new(
           document_path.read,
-          context: env[:context]
+          context: Rundoc::Context::Execution.new(
+            source_path: document_path,
+            output_dir: execution_context.output_dir,
+            screenshots_dirname: execution_context.screenshots_dir,
+            with_contents_dir: execution_context.with_contents_dir
+          )
         ).to_md
 
         if render_result?

test/integration/require_test.rb

@@ -60,4 +60,38 @@ def test_require_runs_code_but_embeds_nothing_if_hidden
       end
     end
   end
+
+  def test_require_is_relative_to_current_file_not_source_file
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do
+        dir = Pathname(dir)
+
+        source_path = dir.join("RUNDOC.md")
+        source_path.write <<~EOF
+          ```
+          :::>> rundoc.require "./src/a.md"
+          ```
+        EOF
+
+        dir.join("src").tap(&:mkpath).join("a.md").write <<~EOF
+          ```
+          :::-> rundoc.require "./b.md"
+          ```
+        EOF
+
+        dir.join("src").join("b.md").write <<~EOF
+          ```
+          :::-> print.text Hello World!
+          ```
+        EOF
+
+        parsed = parse_contents(
+          source_path.read,
+          source_path: source_path
+        )
+        actual = parsed.to_md.gsub(Rundoc::CodeSection::AUTOGEN_WARNING, "")
+        assert_equal "Hello World!", actual.strip
+      end
+    end
+  end
 end