Add identifier, '(', ')', ',' and ';' lexers
Add lexer for string literals
Add Statement and Expression AST node types

The following statements were added:

 - Null statements
 - Expression statements

As well as the following expressions:

 - Reference expression
 - Call expression
 - String literal expression
Implement parser for statements and expressions

The following statements can now be parsed:

 - Null statements
 - Expression statements

As well as the following expressions:

 - Reference expression
 - Call expression
 - String literal expression
Merge branch 'feature-gearc-parsing' into gearc

* feature-gearc-parsing:
  Implement parser for statements and expressions
  Add Statement and Expression AST node types
  Add lexer for string literals
  Add identifier, '(', ')', ',' and ';' lexers