travis: switch to diagrams-travis
clean up some warnings

There are still warnings in the CmdLine module, but I left that alone
since it is likely to change soon anyway.
travis: turn off email notification
Merge branch 'master' of github.com:diagrams/diagrams-postscript into optparse
Implement typeclasses for mainWith.

The idea is to allow users to create programs that generate diagrams
based on some parameters taken on the command line.  This also allows
for a single `mainWith` that can handle a single diagram, multiple named
diagrams, diagrams for each page, or animations with numbered output
files.  Arguments can be taken in order from the commandline or with a
custom parser from the command line or with a custom named argument via
the `Parseable` typeclass.

All this is experimental in this branch and I'm working to factor out
the code that will be common to all backends (or useful in general) and
put it in -lib.