Improve CommandProcessing library

[mikee47]

Here's a PR with a few suggestions to improve the CommandProcessing library.

Handling line endings is inconsistent

Running the CommandLine sample on Host we get this:

Sming>statusSming Framework Version : 5.1.0
ESP SDK version : Host-SDK-v1.0
Time = 26/03/2024 08:59:47
System Start Reason : 0
Sming>

On Esp8266 it looks different:

Sming>
statusSming Framework Version : 5.1.0
ESP SDK version : 3.0.3(8427744)
Time = 01/01/1970 06:42:14
System Start Reason : 6
Sming>

This is what it should be:

Sming>status
Sming Framework Version : 5.1.0
ESP SDK version : 3.0.3(8427744)
Time = 01/01/1970 06:42:14
System Start Reason : 6
Sming>

The currentEOL and associated methods seem redundant

The LineBuffer handles "\r", "\n", "\n\r" and "\r\n" the same way, so we can just use that.

command name is stored twice

Using a HashMap means the command name is stored both as a key, and in the Command object.
Let's just use a Vector instead.

localEcho

Private member variable set to true and never changed. Assume intention was isVerbose.

Consuming RAM for string storage

Since name, help and group strings never change, we should keep them in flash and save some RAM.
Best way I've found is storing them all in a single flash block, which requires only 4 bytes in the Command object.
This requires use of a CMDP_STRINGS macro when calling registerCommand.
To minimise disruption for existing code this can be enabled using CMDPROC_FLASHSTRINGS=1.

When using regular Strings, there's also a small saving to be had by storing these together in a CStringArray.

For comparison, here's what system_get_free_heap_size() reports for the CommandLine sample application.
The call is made at the end of init().

Commit	free RAM
Current version using hashmap	51704
After initial tidy	51752
Use Vector	52104
Use CStringArray	52160
Use FlashString	52664

Welcome message not used

This was used by original TelnetServer sample application. Have restored display of welcome message to connecting clients.
Also getting junk on display because of TELNET escape sequences, so filtered those out too.