Zxpy Versions Save

Previously, only a few select ~'...' statements were being printed out, rather than any bash-string without any assignments to its left. This patch version fixes printing logic.

Fixes the previous broken build, refer #19

Refer #18

• __name__ will now be '__main__', just like how it is when running any other file directly
• Passing additional arguments to zxpy command is now supported

Anything passed as an f-string into a bash string will be automatically quoted with shlex.quote.

i.e., ~f'{xyz}' is the same as ~f'{shlex.quote(xyz)}

• Alternate method of invoking shell commands: stdout, stderr, return_code = ~'...'. Fixes #6
• Add a few tests.

• Removes zxpy executable from sys.argv, to mimic default python behaviour (#10)

• Finally figured out the correct way to handle expr transformations. Cleaned up a bunch of AST code.
• Shell strings and shell f-strings should be usable inside call statements now, eg. print(~'echo test')

• Renamed zx.start() to zx.install() for clarity

• Fix using string attributes over bash f-strings, i.e. (~f'...').splitlines()