+Abella 2.0.2

Also removed abella.2.0.0, which is now obsolete
Abella 2.0.2 requires OCaml 4.01.0+
travis: Fix the check for package availability on older opams

turns out there used to be no good way of simply checking this, so I'm just trying to
install with --dry-run and expecting an empty stdout if the package is unavailable
vastly reduce the number of osx tests to reduce the worker backlog
Fix ocaml-version constraint on ppx_tools again.
Addition of portia, a literate programming tool.

Portia is a programmable text processor that allow to extract fragments from a
set of files and recompose some output files from them. It is meant to serve as
a literate programming preprocessor, agnostic to both the format used for the
documentation and the programming language, and thus is adapted to OCaml.

It is itself implemented using literate programming and needs funnelweb
(http://www.ross.net/funnelweb/) for bootstrap.
Merge pull request #2942 from whitequark/fix-ppx_tools

Fix ocaml-version constraint on ppx_tools again
core 112.01.01
add ojs-base 0.2.0
cow.0.8.1: restrict to ocaml < 4.02 per mirage/ocaml-cow#48
added OCamltter 3.0.0
Add mpris.0.1.0

Signed-off-by: John Else <john.else@citrix.com>
add stog 0.14.0
Merge pull request #2946 from johnelse/add-mpris.0.1.0

Add mpris.0.1.0
commit to enforce re-Travis
Merge branch 'master' of https://github.com/OCamlPro/opam-repository
fixed dependency
Remove unstable mirage-www package from the main repo
Merge pull request #2949 from samoht/mirage-www

Remove unstable mirage-www package from the main repo
travis: fix new opam with old compiler availability check