Add require() helper

* Fix #3
Update the demo

* Use brand new requite() helper;
Merge branch 'feature/require' into develop

Implement require() helper
Add helpers for some integer types

* unsigned in
* long
* unsigned long
* long long
* unsigned long long
Update the demo

* use requreULong() for strlen() comparison
Fix code indentation inside demo.c
Update README

* Mention require() helper
Merge branch 'develop'

Add require() helper.
See issue #3 for details.