Support Spreads in AFX

This changes the way props are returned, the props and spreads are now all returned as attributes-array of an afx-node. The attributes can be of type string, expression and spread the first two contain an identifier with the name of the prop. Spreads do not recieve an identifier but only the expression as payload.

Be tolerant towards empty strings that shall be parsed.

Merge pull request #9 from mficzel/task/avoidErrorsForEmptyAfxCode

TASK: Avoid errors if an empty string is parsed

Return NodeList instead of Node

The parser now returns a nodeList instead of a single node as result. This enables the parsing of multiple elements that are not encapsulated in a container.

Throw exceptions on parser errors

The parser behavior is not modified but in case of syntax-errors in the afx-code exceptions of type \PackageFactory\Afx\Exception are thrown.

Initial public release

Merge pull request #4 from mficzel/task/applyPSR2Rules

TASK: Apply PSR2 formatting rules