Add test for splitting text into words

The accessibility metric depends on a set of tokenizer functions which
processes the text. If the result of these functions does not match the
expectation the whole metric will be faulty.

This commit adds a test for splitting a given text into its word. The
test still fails.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Implement split text into words method

I just implemented the split text into words method of the accessibility
metric and it seems to work as expected.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add more tests for the word splitter

Obiously one test is ridicilous too few, so I just added two more.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add test for split text into sentences method

Just added a test for the next method required by the accessibility
metric: splitting a text into sentences.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add more tests for split into sentences method

Just added some more tests. I am curious whether the method should
return an empty array or exactly one sentence if just a word is passed
For now I am assuming an empty array, because one word does not make a
sentence, does it?

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Change sentence splitter method to object method.

It makes more sense to define the splitter method as object method.
After all the library takes some time to initialize the model.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Implement sentence splitter and adjust tests

I implemented the sentence splitter by using the tokenize method of the
Tactful Tokenizer. The results were unexpected. Hence, it needs to be
investigated whether the single clauses or actual sentences are required
for computing the readability.

I have adjusted the tests to fit the results to which I agree at the
moment anyway.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>