Addition of an 'Ini' system

[weshooper]

As a third unit system:

• The Ini system that is based on a 1024-byte kilobyte and uses case-insensitive PHP INI suffixes (K, M, G)

// Implicit selection through parsing
ByteUnits\parse('8K'); // it's an instance of ByteUnits\Ini

It's an uncommon format, but a common problem:

• http://php.net/manual/en/function.ini-get.php#refsect1-function.ini-get-examples
• https://stackoverflow.com/questions/13076480/php-get-actual-maximum-upload-size

Having the solution in a nice, well-tested package such as this, rather than developers copying and pasting the above code and then rewriting tests (or worse, not!) would be useful.