[fix] Throw if Object::read does not receive a string as the first parameter
[dev] Object - improve documentation and its formatting a bit
[fix] Fix conversion of timestamp-like attributes ( pwdLastSet, accountExpires etc. )
[dev] Simplify conversion of variables to arrays

Typecast to array instead of checking if input type is array and doing
manual conversion.
[dev] Update docblock for Link
[new] Schema::isCached() returns the current state of the Schema cache
[fix] Throw if the Schema cache is present and trying to work with Attribute not defined in Schema

Previously it would simply create a new Attribute without any warning.
This is ok if the Schema is not cached, but if we know what's present
then we can give the user a heads-up before trying to write to the
directory server.
[dev] Update changelog for 0.2.1
[dev] Update README with proper version info for Packagist installation
Release version 0.2.1
[dev] Fix description in composer.json
[dev] Update composer.lock
[dev] Refine Exception message for ambiguous results when doing Object::read()
Release version 0.2.1