Fix a syntax error for non-namespaced tags.

Introduced in #d4dda5
Make completion context extracted properly even if it spans multiple lines.

The previous implementation was strictly line based and the context
extracted for later use would not be a complete statement before the cursor.

This prevented the plugin select the correct completion branch in cases like:

    use ArrayObject,
        ArrayIte ...

Or

    $some_long_variable
        ->some ...

and many other cases.
Make subcontext extraction more inteligent. Fixes #25

When generating the "last variable like part of context" known as scontext
the code was too simplistic and got confused by assignments or a parameter
list.