Replace a sequence of <|> with choice.

Replaces `a1 <|> a2 <|> ... <|> an-1 <|> an`
with `choice [ a1, a2, ..., an-1 ] <|> an` in Idris.REPLParser
where `choice` is from package `parsers` module `Text.Parser.Combinators`.

On my machine with ghc 7.8.3 this lead to a decrease in memory usage
during compilation of this module from >7GiB to ~400MiB.
Merge pull request #1686 from projedi/compilation-memory

Replace a sequence of <|> with choice.
Added initial code for new desugaring scheme for copatterns.
Merge branch 'master' into Copatterns