Update json.c

Although the original version works as expected, the argument order should be changed to calloc's signature:
void* calloc (size_t num, size_t size);
http://www.cplusplus.com/reference/cstdlib/calloc/
Solves a gcc warning for 'static' after 'const'.

json.c:192:1: warning: ‘static’ is not at beginning of declaration [-Wold-style-declaration]
 const static long
  ^
Implement optional support for line and block comments
Add name_length field to object values (closes #41)
Merge branch 'bugfix-const-static' of https://github.com/batrick/json-parser into batrick-bugfix-const-static
Merge pull request #33 from holyhead/patch-1

Fix order of calloc call
Add cast to unsigned char when checking for UTF-8 BOM