Refactor collections and results classes for better consistency and fix some issues.

[jails]

Squash #477, Fix typos, rebase on last commit (data branch), rewrite Sqlite3 on top of PDO

Summary :

• Refactoring data collections and results classes for better consistency.
• Fix an issue with Recordset + composite primary key.
• Fix unset in foreach issue (for RecordSet).
• Remove "tricky" syntax : (i.e. $recordset[0]; $recordset->rewind();) witout $recordset[0]; the rewind fail.
• Rewrite Sqlite3 on top of PDO.
• Some tests added for Collections (i.e. composite primary key, unset in foreach, offset get backwards, etc.)
• Specific test cases for Test case for Bug in DocumentArray::offsetSet() #418, Fixing $options array being ignored when using RecordSet::to('json', $options); #117, SQLite everyother row #253.

Warning BC break :
DocumentArray and DocumentSet are here merged into the DocumentSet class

Should i add an empty DocumentArray class extending DocumentSet for keeping backward compatibility ?

[nateabele]

I'm guessing this replaces your previous gigantic pull request? ;-)

[jails]

Indeed ;-)