Various cleanups of the newarch code

[Gouvernathor]

• Better docstrings
• Better practices using context managers (the "with" syntax)
• Better parameter handling
• Better SVG formatting (more line breaks including final linebreak)
• Include the new link in the SVG (not required since the old page redirects to the new one, but still it's better this way)
• Allow passing parameters to the main function for easier testing
• Move the hashing from the builtin hash function, which is intentionally unreliable on strings, to SHA256, to fix the caching of Arch diagrams.

This should not change anything to the generated SVG apart from whitespace and a comment, so the resulting diagram should be exactly the same - this is not applying my "revamp" changes.

This is available on Beta. I will merge this in one week, on may 31st, to make room on Beta for tests to the Flask port including a reimplementation of the OAuth.

[Gouvernathor]

Merged early, as this does not contain any change to the website's interface or to the diagrams, and does not implement major implementation changes, and I need to make room for my OAuth on Flask.