Allow $ as a character to terminate expressions in castext

[sangwinc]

This change will match core Maxima syntax.

[aharjula]

We currently have no multi-statement CAS expressions in CASText, but if we did, those would probably use keyvals as their basis. So the keyval parsing/validation is the place where this matters the most.

One other reason we might want this is the edge case of having multi-statement localised parsing (which we probably do not have a use-case for), where we could move ; to be a list separator and use $ for the statement separator. Like this:

> php cli/parser_tester.php --string="[1 234,56;x^2,3]$ 1  234 x"  --only=FI
Testing with '[1 234,56;x^2,3]$ 1  234 x'

Token output tests:

 FI:
  [ [              , SYMBOL          ,1:1:1,1,]
  [ 1234.56        , FLOAT           ,1:2:2,8,]
  [ ;              , LIST_SEP        ,1:10:10,1,]
  [ x              , ID              ,1:11:11,1,]
  [ ^              , SYMBOL          ,1:12:12,1,]
  [ 2.3            , FLOAT           ,1:13:13,3,]
  [ ]              , SYMBOL          ,1:16:16,1,]
  [ $              , END_TOKEN       ,1:17:17,1,]
  [                , WS              ,1:18:17,1,]
  [ 1              , INT             ,1:19:19,1,]
  [                , WS              ,1:20:19,2,]
  [ 234            , INT             ,1:22:22,3,]
  [                , WS              ,1:25:24,1,]
  [ x              , ID              ,1:26:26,1,]

Parser output tests:

 FI:

  Root:
[1 234,56;x^2,3]$ 1  234 x
-------------------------- MP_Root
----------------           MP_Statement
----------------           MP_List
 --------                  MP_Float 1234.56
          -----            MP_Operation ^
          -                MP_Identifier x
            ---            MP_Float 2.3
                  -------- MP_Statement
                  -------- MP_Operation * [fixspaces]
                  -        MP_Integer 1
                     ----- MP_Operation * [fixspaces]
                     ---   MP_Integer 234
                         - MP_Identifier x
 toString():
[1234.56,x^2.3];1*234*x;

Note the nice fixspaces issue related to space as the digit grouping char, there... basically, single space is digit grouping there but two is no longer valid for that and needs to be fixed...