Add new simple checker for judging

Currently, the check is very simple.

1. We ignores all whitespaces and counts the number of tokens.
   If the answer and the output have different counts of tokens, return `WA`.

2. If at any index of tokens in the answer and the output is different,
   return `WA`.

3. If two tokens are floating, there are consider equal if there absolute
   difference smaller then EPS (default is 1e-6).

By the way, there is also a new status called `EXACTLY`.
If the answer and the output are exactly same, `EXACTLY` would return.
Make filename_pattern support `contest id`