Handling ":" better in feature parsing

* Handling "`:`" better in feature parsing when there is no double following it - if there is a double, it will be used as a scaling value, as per the [CRFsuite docs](http://www.chokkan.org/software/crfsuite/manual.html), otherwise the entire field (even the colon and whatever is after it) is treated as a feature, as was expected in the example.
* Added loading tests.
* Updated README
* Added tests for the examples in README
* Bumped to version 0.5

Corrects issue #4