Try to use polling instead of mio.

[Berrysoft]

@George-Miao you've always want this:)

However I've found some problems:

• The key of Event is said to identify the fd, I don't know whether an fd could be registered with multiple different keys.
• Don't know if it is allowed to add one fd several times with different keys.

Bonus: Closes #67

[George-Miao]

Cool! Also this should bring more platforms into supported list of compio.

[Berrysoft]

Well there's a big problem here: if one fd added with different keys, it will only show up once. That means we cannot perform multiple read operations on one file.

[Berrysoft]

I have to maintain a queue myself to control the interest.

[Berrysoft]

The performance will be poor if one fd registers a lot operations. We can only pop one operation each time.

I have a question: when a fd is readable, how many read operation could we perform? What if it is writable?

@George-Miao

[George-Miao]

I have a question: when a fd is readable, how many read operation could we perform? What if it is writable?

@George-Miao

It really depends on what type of fd is. I think most of the time it only means at most one read/write operation is non blocking.