Removed usage of and reference to attributes and commands which have now been removed.

Updated to reflect that the default value of abbrev is now False.

Bug fixes:
- case_insensitive is no longer a runtime-settable parameter, but it was still listed as such
- Fixed a recursive loop bug when abbreviated commands are enabled and it could get stuck in the editor forever
    - Added additional command abbreviations to the "exclude from history" list
- Fixed argparse_example.py and pirate.py examples

Other changes:
- Organized all attributes used to configure the ParserManager into a single location
- Set the default value of "abbrev" to False (which controls whether or not abbreviated commands are allowed)
    - With good tab-completion of command names, using abbreviated commands isn't a particularly useful feature
    - And it can create problems

- Disabled TravisCI macOS builds because they are heavily backlogged
- Removed a file which should never have been committed
- Updated Sphinx docs to relect that the default_file_name settable parameter no longer exists
- Fixed comment in a unit test
- Fixed a unit test to use os.path.sep for cross-platform compatibility

Sphinx documenation updates, including:
- Extensively re-wrote the "alternatives to cmd2" section as it was many years out of date
- Reworded a few humorous sections in an attempt to be more professional
- Removed reference to command synonyms/aliases which no longer exist
- Added more detail in a couple places
- Minor rewording and bugfixes throughout

Also added a note to cmd2.py about the expected values for doctest only working for Python 2.7.

Also:
- Added locals_in_py to settable parameters to match documentation.
- Added pycon2010 slides back into doc build since they are referenced with :doc:
- Fixed some references in the documentation
- Updated unit tests accordingly