Make #[ink(selector = ..)] take a u32 parameter instead of a string (#928)

* make #[ink(selector = ..)] take an integer instead of a string

Also warn about deprecation if a user still uses the old string parameter.

* update tests for new selector int parameter

* update contract examples for new selector int parameter

* remove unused regex dependency from ink_lang_ir

Also remove unnecessary regex dependency from ink_lang_codegen

* update README for new selector int parameter

Also update namespace parameter description.

* update preliminary release notes

* update spellcheck dict
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