Support parsing escaped characters for PX_Lexer

[woodzn]

Solve the problem that escaped characters cannot be parsed in JSON

test code

#include "PX_Core.h"
#include "PX_Kernel.h"
char buff[1024*1024];
int main() {
	PX_Json json;
	px_memorypool mp;
	char *p="{\"hello\":\"\\\"\"}";
	mp=MP_Create(buff, 1024*1024);
	PX_JsonInitialize(&mp,&json);
	px_bool ok=PX_JsonParse(&json,p);
	if (!ok) {
		printf("JSON parse error\n");
	}
	else {
		const char* v=PX_JsonGetString(&json,"hello");
		printf("%s:%s\n","hello",v);
	}
}

Program output before repair

JSON parse error

Now the program outputs

hello:"