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.

Issue #89: Fix return types on string functions

* remove unnecessary cast

* add test and expected output

* fix return types
* fix type casts on returns

wait and waitpid

Add the basic structures for the netinet/in.h header.

Add some of the basic structures and stub functions for sys/socket.h

Implement strstr() and strpbrk() from string.h

Update cbindgen and fix issues with signal

The sigaction struct should not be a typedef, but the sigset_t struct
should be a typedef.

Update cbindgen to parse modules with a path attribute and revert the
following commits:
 - 996fad70.
 - cfe98ab3.

Actual working tests on strspn and strcspn

Yet another fix for strcspn and strspn.