Solving Issue #775

[Mario1988]

I improved the method add_fragment_to_line to get rid of the unexpected behavior:
If the last character of segment is a soft hyphen I subtract the width of one soft hyphen from the @accumulated_width.

In addition to that I add a Spec for issue #775 and I improved the spec for issue #347.

[practicingruby]

@Mario1988: Can you look into the test suite failure? It may just be a broken mock object, but we need to sort that out before we can merge.

[practicingruby]

I figured out what was causing the test failure: The width of soft hyphens was being computed whenever any fragment was run in any text call, even if the string had no soft hyphens in it. I moved that check into the if segment[-1] == soft_hyphen to solve this problem.

I've merged a squashed version of this patch in 766a534, thanks!

Some notes for future pull requests:

• You have commit access to Prawn, so please build your feature branches off of our main repo rather than a fork. If you had done that, I could have added my commits directly to this pull request, making it easier to see what changes I made, and any other PrawnPDF contributor could have helped revise the pull request, too.
• When you have a refactoring and a fix you want to do, open a separate patch for each. I was confused by the merge conflicts I saw on the changes to the tests for Hyphenation character rendered in last line of each paragraph of column_box #347, because it's unrelated to Problem with soft-hyphens and text-width #775.

These are minor issues, but keeping them in mind will help make my job easier. Thanks again for the fix!