sample data set for testing sentence based evaluation
Implement ApkSenstenceSet to include some ApkSentence

It has following problem when I run it. But this is related with
usage issue to use sentence as a member variable.

The following sentence is incorrect due to the sentence in sentences.txt
including ',' in the middle of it.

FIXME:
<ApkSentence:0x007f9213854f10 @apk_name="org.wopnersoft.unitconverter",
@id="4", @sentence=["Unit Converter is a simple", "user friendly unit
converter."]>