LanguageToolPython 2.6.4

language_tool_python version 2.6.4 includes the following improvements:

• Upgrade to LanguageTool software version 5.6 (see 5.6 release notes here: https://github.com/languagetool-org/languagetool/blob/master/languagetool-standalone/CHANGES.md)
• Better information about killing java process (re #38) - add information to README about using with .. as tool and tool.close() to manage processes
• Better unit test coverage to confirm java processes are properly killed
• Removed some legacy code
• PR #51: Better support for the 'auto' tag in LanguageTool (thanks @minoguep)
• PR #46: Add requirements.txt to manifest (thanks @dcbaker)

Also, we dropped support for Python 3.5, hopefully this doesn't affect anyone too drastically. This was necessary to add typing hints to our code, which hopefully is worth it!