formatter: add {:sanitize} to return song or song [feat]

[lasers]

DO NOT MERGE. An alternative to @dpeukert's #2234.

Pro:

• Works on all modules. Not restricted to music modules.
• Doesn't have to add anything to existing music modules.
• Remove couple of spotify configs.

Con:

• Non-config metadata patterns. I think users might not care. If they do, they can make PR that will help everybody.
• Abuse (?) Not what it was originally for. Got :d, :.2f, :g, :ceil, and now :escape and :sanitize... Lol.

Instruction:

• To use this, just use {title:sanitize}, {album:sanitize} in any modules (music or not).
• You even can use {title:escape,sanitize} too. My testing is limited and short, but everything seems OK.

Default behavior:

• This can be set as default behavior for music modules by adding class Meta or self.py3.update_placeholder_formats in post_config_hook... but if you add them on, there will no way for users to turn them off in the format config. This is same for other placeholders not related to this PR. Just a FYI.

[lasers]

The issue is hardcoded meta words. It'd be ideal to keep them contained to modules only.

I feel like self.py3.sanitize() / self.py3.replace() might be a better choice, but how should the config look like? I'm guessing it should look something like a thresholds dict... A replace or sanitize dictionary with placeholders (keys) + re.compile keywords including meta words (values).

This PR is just something I tried because of placeholders and doing [\?sanitize {placeholder}] sounds bad.

[lasers]

spotify is untested. FYI just in case.

[lasers]

Is this needed? The composites may could be cached. Maybe regex cache only... Something to look into.