Add memory limits

[r13l]

READ-LINE* currently has no maximum line length, but will instead continue to read input until memory is exhausted. While this default should probably not be changed (there may very well be someone somewhere who is reading multi-gigabyte lines), it would enhance stability to allow callers of the library to specify a maximum line length:

(let ((chunga:*max-line-length* 8192))
  (chunga:read-line* stream))

[r13l]

The following program illustrates the problem (using HUNCHENTOOT, which ultimately calls CHUNGA:READ-LINE):

(ql:quickload '("hunchentoot"))
(hunchentoot:start (make-instance 'hunchentoot:easy-acceptor :port 4242))

(let ((sock (make-instance 'sb-bsd-sockets:inet-socket :type :stream :protocol :tcp))
      ss)
  (sb-bsd-sockets:socket-connect sock #(127 0 0 1) 4242)
  (setq ss (sb-bsd-sockets:socket-make-stream sock :output t :input t :buffering :none :element-type 'character :auto-close t))
  (format ss "GET / HTTP/1.0~c~c" #\Return #\Newline)
  (loop (write-char #\a ss)))

[adlai]

I hope you don't hate me just because I commented something that did not obviously accelerate closure of your open pull request.

Do you have any recommended base for bounding the space complexity of time-critical operations? Obviously, any relevant recommendations should be measurably higher than the base of the natural logarithm, because the default is two and to block me from ever commenting on repositories in the organisation owning the repo, like the most reputed orgs on this social network are wont to do.