Move HTTP strings into flash and provide suitable functions

[mikee47]

http-parser - patch update

• place tokens[] into flash memory and use get_token() function instead - doesn't rely on mforce32 compiler support to save RAM
• Remove http_errno_name() - replaced with httpGetErrnoName() defined in HttpCommon.cpp. Note the replacement returns a String, not a const char*

HttpCommon

• Add httpGetErrnoName(), httpGetErrnoDescription() and httpGetStatusText() functions - saves RAM by storing text strings in flash

HttpServerConnection

• getStatus() method removed, superseded by httpGetStatusText() function. The message parameter is now a const String&, instead of const char*. As the default value is nullptr, if () statement works as expected.

FlashString.h

• Add FSTR_TABLE macro

Samples/Basic_Progmem

• Add demo code for use of FSTR_TABLE

[mikee47]

Saves > 4K of RAM. Test code:

#include "Network/Http/HttpCommon.h"

void testHttpCommon()
{
	for (int i = 0; i < 100; ++i) {
		auto err = static_cast<http_errno>(i);
		debug_i("httpError(%d) = \"%s\", \"%s\"", i, httpGetErrnoName(err).c_str(),
			httpGetErrnoDescription(err).c_str());
	}

	for (int i = 100; i < 550; ++i) {
		debug_i("http_status(%d) = \"%s\"", i, httpGetStatusText(i).c_str());
	}

}

[slaff]

Looks good but small changes are needed.

[mikee47]

Closes #1173