Migration guide for the switch from 1.0.0 to 2.0.0

[FSMaxB]

Because there's so many changes in the new release, a migration guide is needed that explains the steps of how to migrate existing code to the new version.

[FSMaxB]

Roughly these steps:

• replace valueint and valuedouble with number
  • if valueint is used, typecast number to int instead
• replace string with name
• replace valuestring with string
• replace prev with previous
• pass a pointer to an instance of cJSON_Hooks to the functions instead of using cJSON_InitHooks
• pass a pointer to a char* to the functions instead of using cJSON_GetErrorPtr

[DaveGamble]

if valueint is used, typecast number to int instead

May I encourage the addition of a function that simply casts the return value, to simplify the transition?

pass a pointer to a char* to the functions instead of using cJSON_GetErrorPtr

If you replace cJSON_Parse with cJSON_ParseWithOpts, then you just need to remove cJSON_GetErrorPtr.