`AsciiString`s ascii-ness is a rust safty issue

[rustonaut]

AsciiString guarantees on a type level that it's actually only ascii, if it contains non ascii it is a rust saefty violation.

• We don't need such strict guarantees.
• we have a lot unsafe or inefficient code to convert to AsciiString
  • this unsafetiness is not needed at all
• a violation of ascii ness can be "just" an error in the produced output bug, but with the guarantees on safety level such a bug has the (theoretical) potential to cause undefined behavior with all up to catastrophic consequences (through it probably will just work out due to how we use it and the the fact ascii chars are repr(u8) but we can't rely on it)

[rustonaut]

Replaces ascii with soft-ascii-string and removed a ton of unsafe code