Added functions for stdio.h

implement rand and srand using the rand crate

unistd: add a preliminary implementation of getopt()

refactor nanosleep

Implement strtok

implement bsearch

Add some of the basics for netinet/in.h and sys/socket.h

Use build matrix on Travis CI

This makes it easy to see which target failed to build.

Removed all function pointers in FILE, moved internal functions to be member functions of FILE, made relevant *mut FILEs into &mut FILE and made suitable functions safe again

Issue #89: Fix return types on string functions