refactor process.c

- include api.h instead of individual #includes
- moved metatable name to API_TYPE_PROCESS
- moved read buffer size to READ_BUF_SIZE

src/api/api.h

@@ -7,6 +7,7 @@
 
 #define API_TYPE_FONT "Font"
 #define API_TYPE_REPLACE "Replace"
+#define API_TYPE_PROCESS "Process"
 
 void api_load_libs(lua_State *L);