Resolving issues in merge request

system_calls.h
line 38: Fixed return type for syscall_filesize
syscall_filesize.c
line 12..14: Rewrote to fix undefined function and to condense the code
line 14: Added function to search for files in memory
syscall.c
line 77: Added file_search function skeleton
syscall.h
line 6: Added file_search declaration