bshell: re-organise build into three separate components

bshell: the front-end binary
bshell.runtime: contains the parser, compiler, and classes needed to run bshell scripts
bshell.core: contains the builtin commandlets and aliases

bshell.runtime/ast/word.c

@@ -0,0 +1,15 @@
+#include <bshell/ast.h>
+#include <bshell/parse/token.h>
+
+static void to_string(const struct bshell_ast_node *node, fx_bstr *out)
+{
+	const struct bshell_word_ast_node *word = (const struct
+	                                           bshell_word_ast_node *)node;
+	fx_bstr_write_fmt(out, NULL, "%s", word->n_value->tok_str);
+}
+
+struct bshell_ast_node_definition word_bshell_ast_node = {
+	.def_id = BSHELL_AST_WORD,
+	.def_node_size = sizeof(struct bshell_word_ast_node),
+	.def_to_string = to_string,
+};