[Refactor] Move parsing of {, } and : symbols to the Block syntax module

[Ph0enixKM]

EBNF explanation

Right now when parsing let's say if loop we perform the following EBNF:

block = { statement } ;
if_cond = 'if', condition, (':' | '{'), block, {'}'} ;
(* ... *)

Let's change this to:

block_multi = ':', statement ;
block_single = '{', { statement }, '}' ;
block = block_multi | block_single ;
if_cond = 'if', condition, block;
(* ... *)

Non-EBNF explanation

Basically let's handle parsing of tokens like {, } and : in Block syntax module so that when we use it later we remember to handle the both syntaxes { .. } and : as well.