v1.0.2.0: Add support for GHC 7.10 & base-4.8

This add missing `Functor` & `Applicative` instances for `P` and
`Lex` (and `DocM`) monads needed for AMP compatibility.

The package version is minor-bumped to v1.0.2.0 since new instances were
added to the exposed API.

Moreover, a Hackage-compliant changelog file is added as
extra-source-files.