Fixed examples for changes in lexer

Name assigned to %CONST is the next symbol in stream, not the symbol
attached to it.

asm/lexer.cpp

@@ -50,7 +50,7 @@ pair<token_t, lerr_t> tokenise_symbol(string_view &source, size_t &column,
 
   token_t t{};
 
-  if (initial_match(sym, "%CONST"))
+  if (sym == "%CONST")
   {
     t.type = token_type_t::PP_CONST;
   }

examples/factorial.asm

@@ -6,7 +6,7 @@
   ;; 65 which means that past 20! results are truncated and therefore
   ;; the program produces inaccurate factorials.
 
-  %const(limit) 20 %end
+  %const limit 20 %end
 
   ;; Setup entrypoint
   global main

examples/fib.asm

@@ -5,26 +5,26 @@
 ;;; stack version.
 
   ;; Constants
-  %const(limit) 93 %end
+  %const limit 93 %end
 
-  %const(increment_i)
+  %const increment_i
   push.reg.word 2
   push.word 1
   plus.word
   mov.word 2
   %end
 
-  %const(print_i)
+  %const print_i
   push.reg.word 2
   print.word
   %end
 
-  %const(print_reg_0)
+  %const print_reg_0
   push.reg.word 0
   print.word
   %end
 
-  %const(print_reg_1)
+  %const print_reg_1
   push.reg.word 1
   print.word
   %end