This avoids having to escape | or &, though we still allow that for
the deprecation period.
To detect deprecated usage, we insist that alternatives are *always*
an array (which could be loosened later), but that also means that
restrictions must *always* be an array for now.
Before:
```
# invoice, description either A or B
lightning-cli commando-rune '["method=invoice","pnamedescription=A|pnamedescription=B"]'
# invoice, description literally 'A|B'
lightning-cli commando-rune '["method=invoice","pnamedescription=A\\|B"]'
```
After:
```
# invoice, description either A or B
lightning-cli commando-rune '[["method=invoice"],["pnamedescription=A", "pnamedescription=B"]]'
# invoice, description literally 'A|B'
lightning-cli commando-rune '[["method=invoice"],["pnamedescription=A|B"]]'
```
Changelog-Deprecated: JSON-RPC: `commando-rune` restrictions is always an array, each element an array of alternatives. Replaces a string with `|`-separators, so no escaping necessary except for `\\`.
Rusty Russell