Allow nested loopBlocks

- loopBlocks now contain statements i.o. instructions

src/grammars/mblf.pest

@@ -1,15 +1,17 @@
 operator       = @{ "operator" } // TODO
 operand        = @{ "operand" }  // TODO
 
-instruction = { operator ~ (" "+ ~ operand)*}
+instruction    = { operator ~ (" "+ ~ operand)* }
 
 loopBlockStart = { "[" }
 loopBlockEnd   = { "]" }
 loopBlock      = { loopBlockStart
-            ~ instruction*
+                 ~ statements
                  ~ loopBlockEnd
-}
+                 }
 
 statement      = _{ instruction | loopBlock }
+statements     = _{ statement* }
+
 
 file = {SOI ~ (statement ~ ("\n" | "\r\n")+)* ~ EOI}