The `no_std` feature has been broken since version `0.14`, since it did
not disable the `std` feature of `memchr`.

To fall more in line with the general ecosystem standards, this crate
changes the `no_std` feature into an `std` feature. Since `vte` should
be significantly faster with this feature, it has also been enabled by
default (previously `no_std` was default).

This is a breaking change, even if we ignore `no_std` consumers which
aren't able to compile 0.14, since intermediate dependencies relying on
the `no_std` feature will have to remove it from the manifest.

See https://vt100.net/docs/vt510-rm/DECST8C.html.

The table based state change was too complex to make guesses why it's
getting slow and too fragile, as in modifying the amount of
states/actions were slowing down, even though, they were not used.

Rewrite the state + action change exactly how it's in [1] with respect
to our modifications/C1, etc. The new implementation is generally faster
than the previous one and is easier for compiler to reason about and
generate more efficient structures.

Also, the structure got way simpler to follow, since it matches the
spec pretty much exactly.

[1] - https://vt100.net/emu/dec_ansi_parser

If the valid character was split across reads of partial utf8 and
got terminated by invalid byte, we should print it and advance, instead
of trying to discard it entirely.

This patch overhauls the `Parser::advance` API to operate on byte slices
instead of individual bytes, which allows for additional performance
optimizations.

VTE does not support C1 escapes and C0 escapes always start with an
escape character. This makes it possible to simplify processing if a
byte stream is determined to not contain any escapes. The `memchr` crate
provides a battle-tested implementation for SIMD-accelerated byte
searches, which is why this implementation makes use of it.

VTE also only supports UTF8 characters in the ground state, which means
that the new non-escape parsing path is able to rely completely on STD's
`str::from_utf8` since `memchr` gives us the full length of the plain
text character buffer. This allows us to completely remove `utf8parse`
and all related code.

We also make use of `memchr` in the synchronized escape handling in
`ansi.rs`, since it relies heavily on scanning large amounts of text for
the extension/termination escape sequences.

Instead of collecting all the data into the vector just dispatch it
right away avoiding allocations.