fix(parser): fail closed on unsupported command syntax (#348)

* fix(parser): preserve escaped reserved words

* fix(parser): fail closed on unsupported command syntax

* fix(parser): handle recursive timing prefixes

* fix(parser): preserve timing prefix grammar

* fix(parser): preserve leading negation timing

* fix: preserve escaped word semantics

* fix(parser): preserve command-start grammar

* fix(interpreter): preserve compgen wordlist escapes

* fix(parser): reject bare in

* fix(parser): preserve quoted subscript escapes

* fix(parser): preserve escaped subscript parameters

* fix(parser): preserve escaped subscript quotes