* Adds support for custom where bounds

The user can now specify a custom where bound when using the derive
macros:

- `#[codec(encode_bound(T: Encode))]` for `Encode`
- `#[codec(decode_bound(T: Encode))]` for `Decode`

If nothing is specified (`encode_bound()`) the where bounds will be empty.

* Apply suggestions from code review

* Apply suggestions from code review

Co-authored-by: Gavin Wood <gavin@parity.io>

* Switch array impls to const generics

* addr comments

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: David <dvdplm@gmail.com>

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Andronik Ordian <write@reusable.software>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: David <dvdplm@gmail.com>

* CI: add miri test; new phase; remoe CARGO_HOME cache

* add miri and falgs to test

* Update .gitlab-ci.yml

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

Co-authored-by: Cheme
Co-authored-by: Brian Anderson <andersrb@gmail.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: David <dvdplm@gmail.com>

* change (CI): cache pre-population script; use of cargo home and cargo target caches; rules instead only

* fix (CI): wrong pasta

* fix (CI): persimmons to the pre_pop script

This makes it easier to write code that uses `Error` with or without `std`.

Seek trait doesn't ensure that the length is fixed, thus our usage in IoReader is wrong. Now fixed.

* fix

* better impl

Normally, the span of a field has the same hygiene context as
`Span::call_site`. However, it's possible for a struct definition
to be 'constructed' via a `macro_rules` macro such that the field
has a different hygiene context. This will cause the expanded code
to be unable to resolve any references to `self`, resulting in a
compilation error.

This pull request uses `quote!` instead of `quote_spanned!` when
emitting a 'self' identifier. `quote_spanned!` is still used for
everything else in the emitted method, meaning that error messages
will still point to the proper field.

I've included a test case which triggers this issue on
Rust 1.43.1. It's current difficult to hit this issue
other than in this artificial case, but that will change
once rust-lang/rust#72622 is re-landed.

* decode_length for tuple'

* add test

* refactor

* Verify bytes after encoding an object that was decoded from original bytes

* Add BinaryHeapWrapper to allow PartialEq trait impl

* Add Arbitrary crate and derives

* Add prototype for encoding testing

* Add partial encode fuzz testing

* Derive arbitrary to compact

* Add types for encode fuzzing

* Simplify macro

* Remove BitVec from Encoding macro

* Add comments about sorting

* Add comment for BinaryHeapWrapper

* Update bytes sorting and move type display to the end

* Make raw1 immutable

* Hide arbitrary crate behind feature 'fuzz'

* Indent macro

* Impl Arbitrary for BitVecWrapper

* Differentiate flows depending on fuzzing input

* Update comments and add TODO

* Change minimal to only_decode

* Use more straightforward code for defining eq trait

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Put comments before derive

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Put comments before derive

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Use match in macros; Remove comments on into_iter_sorted and fix compile for paritaleq trait

* Use match in fuzz_encode

* Fix typo in comments

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Remove useless mut

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* add check for attribute and modify index attribute

* fmt

* improve doc

* improve doc

* add custom error message

* add Encode and Decode impls for NonZero* types

* fix Wasm32 build for Error instantiation

* apply code review requests

* impl return error for decode_from in CompactAs trait

* update readme

* update doc test and readme

* Change from_utf8_lossy to from_utf8 to avoid replacement characters

* Compact code to make it clearer

* Add invalid utf8 string decode

* Fix code for no-std

Fixed link to `Compact Integers`