Add properties to Function to check function flags.
Add properties to Function to check function flags.

Why:

* It is easier to check booleans than having to lookup what the function
  flags are.

This change addresses the need by:

* Adds a property to `function.Function` for each function flag defined
  in `function.FUNC_FLAGS`.
    * is_noret: Function doesn't return
    * is_far: Is a far function.
    * is_library: Is a library function.
    * is_static: Is a static function.
    * is_frame: Function uses frame pointer (BP)
    * is_user_far: User has specified far-ness of the function.
    * is_hidden: A hidden function chunk.
    * is_thunk: Thunk (jump) function.
    * is_bottom_bp: BP points to the bottom of the stack frame.
    * is_noret_pending: Function 'non-return' analysis must be performed.
    * is_sp_ready: SP-analysis has been performed.
    * is_purged_ok: 'argsize' field has been validated.
    * is_tail: This is a function tail.

tmr232/Sark,tmr232/Sark