Created example for frontend in Pascal

[AlexandraNegoita]

• initialized ANTLR;
• input file with Pascal code is 'code-pascal.txt';
• created lexer, parser;
• imported packages '@easycompiler/ast' and '@easycompiler/frontend' - doesn't work
• implemented Frontend from interface IFrontend - parse will contain all token visitors

[AlexandraNegoita]

In Pascal example:
Updates:

• added entire pascal test program
• class pascalVisitors, for each node that the compiler reaches in the example program (using Pascal grammar)
• node types are mostly made Block, until further addition of nodes to AST package
• added implementation of the frontend interface
  Problems:
• JSON printing shows four Value nodes with "Hello, World", the parsing is correct

In AST package:
Updates:

• added parseJSON method to all nodes, for JSON clarity
• added Value node, that will store all types of values used in the program
• added name property to the Block node, for JSON clarity
• modified Type node to set with string property
• added string definitions to enum NodeID, for JSON clarity