Misc fixes for ink! 3.0-rc1 (#530)

* [benches] fix lazy benchmarks

* [*] fix Cargo.toml documentation links

* [readme] show CI status of master branch always

* [readme] misc improvements

* [storage] make re-export of LazyHashMap inline

* [releases] add notes about ink_core split

* [allocator] add some crate level docs

* [storage] impl scale_info::TypeInfo for ink_storage::alloc::Box

* [metadata] improve docs slightly

* [storage] re-introduce StorageLayout impl for storage::Box
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