rokucommunity / brs / #29

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feat(lex,parse): Add stub try/catch implementation (#34)

* feat(lex): Emit try/catch/throw lexemes for parsing

RBI 9.4 adds support for error handling via the `try`/`catch` model [1].
Interestingly, `try`, `catch`, and `endtry` are all valid identifiers!
That makes parsing a little bit tougher, but it's not unprecedented in
this language.  Detect `try`/`catch`/throw`/`end try` during lexing and
emit the proper lexemes.

[1] https://developer.roku.com/docs/references/brightscript/language/error-handling.html
see #554

* feat(parse): Consume try, catch, and end try lexemes

Throwing exceptions and catching them aren't yet supported in `brs`, so
executing only the `try` block seems to be a reasonable "bare minimum"
approach to try/catch support.  Handle `try`, `catch`, and `end try`
lexemes in the parser, emitting TryCatch statements for the interpreter
to execute naïvely.

see #554

* Fixed Test Case

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Co-authored-by: Sean Barag <sean.barag@hulu.com>
Co-authored-by: Bronley Plumb <bronley@gmail.com>

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