- convert to singlespec

- update to 0.7.5:
* `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
* Fixed argparse_example.py and pirate.py examples and transcript_regex.txt transcript
* Fixed a bug in a unit test which occurred under unusual circumstances
* 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)
* Improved implementation of `load` to use command queue instead of nested inner loop
* Fixed a couple bugs in interacting with pastebuffer/clipboard on macOS and Linux
* Fixed a couple bugs in edit and save commands if called when history is empty
* Ability to pipe ``cmd2`` command output to a shell command is now more reliable, particularly on Windows
* Fixed a bug in ``pyscript`` command on Windows related to ``\`` being interpreted as an escape
* Ensure that path and shell command tab-completion results are alphabetically sorted
* Removed feature for load command to load scripts from URLS
* Removed presence of a default file name and default file extension
* ``load`` command has better error checking and reporting
* Clipboard copy and paste functionality is now handled by the **pyperclip** module
* ``shell`` command now supports redirection and piping of output
* Added a lot of unit tests
* Removed pause command
* Added a dependency on the **pyperclip** module
* Fixed a bug in displaying a span of history items when only an end index is supplied
* Fixed a bug which caused transcript test failures to display twice
* Added the ability to exclude commands from the help menu (**eof** included by default)
* Redundant **list** command removed and features merged into **history** command
* Added **pyscript** command which supports tab-completion and running Python scripts with arguments
* Improved tab-completion of file system paths, command names, and shell commands
* Changed default value of USE_ARG_LIST to True - this affects the beavhior of all **@options** commands