Qt CodeEditor: Honor `show_line_numbers` and `readonly` style.
Fix travis ci tests (add pygments dependency for code editor)
Merge pull request #145 from pankajp/qt-codeeditor-honor-line-number-widget

Qt CodeEditor: Honor `show_line_numbers` and `readonly`.
Remove deprecated `implements` declaration, use `provides` instead.
Update CHANGES.txt.
Merge pull request #152 from enthought/provides-beats-implements

Remove deprecated `implements` declaration, use `provides` instead.
Merge https://github.com/enthought/traitsui into python3