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/double.c

@@ -0,0 +1,16 @@
+#include <bshell/ast.h>
+#include <bshell/parse/token.h>
+#include <fx/stream.h>
+
+static void to_string(const struct bshell_ast_node *node, fx_bstr *out)
+{
+	struct bshell_double_ast_node *i = (struct bshell_double_ast_node *)
+		node;
+	fx_value_to_string(&i->n_value->tok_number, (fx_stream *)out, NULL);
+}
+
+struct bshell_ast_node_definition double_bshell_ast_node = {
+	.def_id = BSHELL_AST_DOUBLE,
+	.def_node_size = sizeof(struct bshell_double_ast_node),
+	.def_to_string = to_string,
+};