Create eep-0063.md: Lightweight UTF-8 binary string literals and patterns

eeps/eep-0063.md

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+    Author: Tom Davies <todavies5(at)gmail(dot)com>
+    Status: Draft
+    Type: Standards Track
+    Created: 1-Jun-2023
+    Post-History:
+****
+EEP 63: Lightweight UTF-8 binary string literals and patterns
+----
+
+Abstract
+========
+
+This EEP proposes new syntax for UTF-8 binary string literals and patterns to bring them
+into line with list-strings.
+
+List-strings (i.e. strings represented by lists of unicode codepoints) have a
+convenient syntax: `"This is my string"`, but the corresponding syntax for
+UTF-8 encoded binary strings is more cumbersome: `<<"This is my string"/utf8>>`.
+
+Here, we propose a lightweight, alternative syntax for UTF-8 binary string literals:
+
+```
+Str = b"This is my string".
+```
+
+and patterns:
+
+```
+case Str of
+  b"This is my string" -> ok;
+  _ -> error
+end.
+```
+
+Implementation outline
+==============
+
+Early during compilation and shell evaluation, the new syntax would be desugared to
+the corresponding existing syntax, e.g. `b"This is my string"` is rewritten to
+`<<"This is my string"/utf8>>`.
+
+Reference Implementation
+========
+
+TBD
+
+Backward compatibility
+========
+
+The new syntax is invalid in older releases, so would not impact existing code.
+
+The implementation of the new syntax would purely be via an early re-writing step,
+so would be desugared to the existing representation before later compiler stages.
+This would mean bytecode would be unaffected, but debugging/AST data would reflect
+the new source represenation.
+
+Copyright
+=========
+
+This document is placed in the public domain or under the CC0-1.0-Universal
+license, whichever is more permissive.