Improve usability/factorization of bufferedConnection

[devyte]

The bufferedConnection code has been pulled out into its own file. This improves usability, but the result needs more work.
Specifically, usage depends on a socket onSent() callback, which is outside the bufferedConnection file, and on coroutine creation/handling/destruction code, which are also outside the bufferedConnection file.
The ideal buffered connection would have a usage model as close as possible to the current socket usage model, have all the coroutine code hidden away, have a small mem footprint, and trivial to integrate into an application for general use.
I would suggest creating something along the lines of another class which wraps the bufferedConnection, maybe called a "threaded" connection, which contains the missing pieces of dependent code. This is just an idea of course, and open for discussion.

[devyte]

I have a solution that encapsulates the bufferedConnection as well as the whole coroutine uglyness. Please see nodemcu-platform, file tbconnection.lua, and httpserver for usage. The encapsulation is a threaded-buffered connection. It is constructed with a normal connection, and has a :run() method that receives as arguments a function and optional arguments to pass to the function. The function passed as argument receives as first argument a buffered connection and the optional arguments passed to run(). Inside of it, you can :send() all you wish, the payloads will be buffered into chunks of threshold sice (currently set to 256 bytes), and then they get flush()ed and physically sent.
Example:
local function servefunc(bconn, msg)
bconn:send(msg)
end

local msg = "hello nodemcu"
local tbconn = dofile("tbconnection.lc")(connection)
tbconn:run(servefunc, msg)

It seems to work, but mem footprint is along the lines of 6K, which is large, so any ideas to reduce it are welcome. @marcoskirsch @pjsg I think it solves this issue, but you'd have to pick it up and integrate it into this repo.