Various Updates and Fixes

[erbius]

I have made the following updates:
Two new CLI flags
-x hides the banner, author name, version, usage etc.
-f saves any found emails to a file specified by the user.
Removed explicit thread count. By not specifying ThreadPoolExecutor will make the count (current processors*5)
Updated banner info code to make use of a multi-line f-string.
Updated requirements.txt to use the latest versions.

Style changes:
Updated many stdout messages to have capital first letter
No longer prints done; if finds emails display message else display " did not find" message
Updated message if no emails found.

This is my first ever PR, I have only been learning Python 3 for the last 2 weeks.
Please let me know if these changes are not suitable or need further amendment.