Added WebSerialLite: a lightweight high-performance version of WebSerial

[mathieucarbou]

This is how I use WebSerial in my projects. I have a mechanism to stream Arduino logs to both Serial and WebSerial.

I need real-time and speed, I cannot buffer since I would lose some precious logging happening just before an ESP restart for example.

In this PR I've ported the building bricks for such use case in this project:

• WebSerialLite is able to stream in real-time at a speed of more than 20 messages per second with a low memory footprint
• There is no synchronization or mutex in place (be careful when 2 cores are writing)
• There is no buffering by default, so write(c), print(c), printf(...) and variants with only 1 character are not allowed
• WebSerialLite can use a special line buffering mode to only send complete lines to the browser - suitable for redirecting Arduino logs to the browser

[mathieucarbou]

Additional note: I will look to add that in the pro version and my projects, but as mentioned in #79, not having a command history in the free version is really a blocker to integrate it in some others.

[ayushsharma82]

@mathieucarbou , Let's integrate it as an switch with macro. So those who want to use it can switch the implementation with setting the macro to 1. Having two different classes is difficult for me to explain and keep in a product.

[mathieucarbou]

OK I will review the PR soon

[mathieucarbou]

@ayushsharma82 : PR ready to review and includes #81

I made it in a way that the public methods are the same, and we can switch the flag without having to update the code. In example, in the high perf version, the loop() is a no-op.

I struggled for the Arduino CI and gave up. Apparently it is not possible to set extra build flags because setting them would override the ones from the platforms.txt (build.extra_flags=-DESP8266) and consequently loose the information about the platform type. And since the same run command is used for several env (matrix build), I cannot fix it.

But in any case, we have the PIO build which is easier to maintain and run fine with and without the flag.

I also manually tested both versions with 2 examples.

[ayushsharma82]

Looks really good! 👍🏻