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/parse/syntax/expr.c

@@ -0,0 +1,15 @@
+#include "../syntax.h"
+
+bool parse_expr(struct bshell_parse_ctx *ctx, struct bshell_ast_node **out)
+{
+	bool ok = false;
+	if (!ok && peek_arith_expr(ctx)) {
+		ok = parse_arith_expr(ctx, BSHELL_PRECEDENCE_MINIMUM, out);
+	}
+
+	if (!ok && peek_command(ctx)) {
+		ok = parse_command(ctx, out);
+	}
+
+	return ok;
+}