fix escape codes splitting across getBlockOfChars

[goertzenator]

This patch adds a 20ms timeout to getBlockOfChars when an ESC character is seen. This forces getBlockOfChars to wait for a whole escape sequence which could otherwise get fragmented on a slow connection.

Some useful reference information on this topic:
https://stackoverflow.com/a/3219355/398021

Fixes issue #160

[Bodigrim]

haskeline is a GHC boot library, it cannot depend on async unfortunately.

[goertzenator]

I don't have time to dive into this right now but I would like to lay out a few thoughts:

• It would be worth looking at some other mature terminal program such as Putty software to see how the ESC character is managed.
• An incremental parser like the one found in the binary package might be the right approach. Pair that with a timeout symbol injected into the input stream to distinguish a naked ESC from an unfinished ESC code. This is of course a more significant change.
• The current PR only addresses Posix. A complete fix would also address Win32, but I have not looked closely enough at the Win32 code to see if it is even affected.

edit: fixed Putty nonsense.. I was thinking at the wrong end.

[goertzenator]

Excerpt from https://www.man7.org/linux/man-pages/man3/readline.3.html . So readline appears to default to a very large timeout of 500ms.

       keyseq-timeout (500)
              Specifies the duration readline will wait for a character
              when reading an ambiguous key sequence (one that can form a
              complete key sequence using the input read so far, or can
              take additional input to complete a longer key sequence).
              If no input is received within the timeout, readline will
              use the shorter but complete key sequence.  The value is
              specified in milliseconds, so a value of 1000 means that
              readline will wait one second for additional input.  If
              this variable is set to a value less than or equal to zero,
              or to a non-numeric value, readline will wait until another
              key is pressed to decide which key sequence to complete.```

[goertzenator]

Another data point from rustyline. This library allows you to specify the timeout:

https://github.com/kkawakam/rustyline/blob/91f616a1c8e3208cffae7d9912446f850474d65f/src/config.rs#L545-L556