Improve filter option in copySync

[manidlou]

Applied the improved filter option that introduced in #423 to copySync().

Also cleaned up copySync a bit including:

• removed recursive option. This option never been documented and had no use.
• Add copyFileSync() as a function and wrap everything in one file since the entire file is just 114 lines!

In addition, removed option.overwrite = false in moveSync() since one of the tests (when move directory and overwrite is true) wouldn't pass. It was weird though as it would pass before! 😕 IDK! maybe because of the closure! After all, I guess it's better to remove that line though. Please correct me if I am wrong 😬

[coveralls]

Coverage decreased (-0.4%) to 86.511% when pulling 56c814e on filter-copySync into 44eb2c3 on master.

[manidlou]

closing this since filter option is going through major changes in rewrite of copy that will affect copySync as well because of consistency.