Refactor, add extensive README.md, add future planning

src/Program/Builder/ProgramBuilder.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace Program\Builder;
+
+use Program\Block;
+use Program\Program;
+use Program\Word;
+use RuntimeException;
+
+class ProgramBuilder
+{
+	/**
+	 * @param Word[] $words
+	 * @return Program
+	 */
+	public function build(array $words): Program
+	{
+		$firstWord = array_shift($words);
+		if (!preg_match('/^N9\d\d\d$/i', $firstWord)) {
+			throw new RuntimeException('Expected program number (N9xxx), got ' . $firstWord);
+		}
+
+		$program = new Program($firstWord->value);
+
+		$blockBuffer = null;
+		while ($word = array_shift($words)) {
+			if ($word->register === 'N') {
+				if (!is_null($blockBuffer)) {
+					$program->addBlock($blockBuffer);
+				}
+				$blockBuffer = new Block($word->value);
+				continue;
+			}
+			$blockBuffer->addWord($word);
+		}
+		if (!is_null($blockBuffer)) {
+			$program->addBlock($blockBuffer);
+		}
+
+		return $program;
+	}
+}