Release new sem. version

[NoHomey]

I would like to request a new sem. version release. Since all commits after 2.1.1 are result of mine pull requests beeing merged I would like to update both thе DOCUMENTATION.md and CHANGELOG.md so new version could be released. But first #51 needs to be closed.

New version is needed because of the following issues have been fixed since 2.1.1:

• Fixing in which ints pinmodeAlt mode is checked, [https://github.com/eugeneware/wiring-pi/commit/24b09083ac5842a914e3369d5af69a4a3bf4bcba]
• All WiringPi WPI_MODE_* constants are now exported, [https://github.com/eugeneware/wiring-pi/commit/e60dc3fd73ce5c48664ede14ab1c9d599796ce44]
• sn3218 extention has been made available, (closes #42), [https://github.com/eugeneware/wiring-pi/commit/6931958c392968dd53d06cc39b133a6d852d0f46]
• all file descriptors opened by wiring-pi are now releasable, (closes #43 ) [https://github.com/eugeneware/wiring-pi/commit/bf14d466b56761d5de40511549fbcd8b6c6ebe0c]

[nekuz0r]

I will update the changelog accordingly to your fixes/additions this evening and bump the version to 2.2.0

[nekuz0r]

Thanks a lot for your contributions, much appreciated 💯