Support "Single Line" variable declarations

[ghaith]

Is your feature request related to a problem? Please describe.
The Standard allows the declaration of variables in a single statement
Example:

VAR
  var1,var2,var3 : INT;
END_VAR

Creates 3 variables of type INT
We should support this in the parser.

Describe the solution you'd like
During parsing, add a variable for every entry in the list.

Alternative Idea:
Instead of saving each variable in an entry, we could make the AST support variable lists per declaration. This might be better in regards to inline declared types e.g. ARRAY OF but might be more complex on the AST