lib1515.c: Fixed various compilation warnings

lib1515.c:38:26 warning: unused parameter 'curl'
lib1515.c:38:81 warning: unused parameter 'ptr'
lib1515.c:38:5 warning: no previous prototype for 'debug_callback'
lib1515.c:46:5 warning: no previous prototype for 'do_one_request'
lib1515.c:120:3  warning: ISO C90 forbids mixed declarations and code

As well as some code policing such as white space and braces.