Decide on which Checkers to implement

[XOSplicer]

So far as examples:

• module definitions with a single statement should be inside "{}"
• module instantiations with single statements should be inside "{}"
• variable names should not start with "$" if they are no reserved variables ($fa etc)
• built-in modules should not be overwritten
• built-in functions should not be overwritten
• number of statements in a module should not exceed 50
• number of statements in a file should not exceed 200