add `choice` combinator for Lexers
add `choice` combinator for Lexers

The argument to `choice` must be a non-empty `List Lexer`.

uuhan/Idris-dev,uuhan/Idris-dev,kojiromike/Idris-dev,uuhan/Idris-dev,uuhan/Idris-dev,uuhan/Idris-dev,uuhan/Idris-dev,kojiromike/Idris-dev,uuhan/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev