Implement a "Hello World" checker pass

[rachitnigam]

Implement a simple checker pass that prints out "In a for loop" and "In an array access" when appropriate.

• Use the checker framework.
  • A checker needs to define an environment that is used to collect information about the program by assigning the type Env.
  • It also needs to describe an empty environment by defining val emptyEnv

Example:

• WellFormedness Check: A simple pass which an empty environment that just checks the program. It does not build up any information.
• DependentLoop Check: A pass that checks loop dependencies. It builds an environment and uses it to keep track of information about variables.
• The passes folder defines other checkers used by the compiler.