BNFC 2.9: cleanup, introducing breaking changes

[andreasabel]

This is an umbrella issues collecting breaking changes we might want to introduce in BNFC. The goal is to remove exotic features and make BNFC more robust.

More permissive license (see #308):

• [x] Change to BSD-3

LBNF:

• [x] Remove profiles?
• [x] Remove views?

Haskell backend:

• [x] Remove ErrM, use Either and ExceptT instead (already in 2.8.4)
• [ ] Use a standard pretty-printing framework for the printer instead of the own hand-rolled one
• [x] Drop Alex1 and Alex2 (Peter Gammie) support and --sharestrings (Björn Bringert)
• [ ] Make -d option default
• [ ] Make --ghc option default and drop support for non-GHC Haskell in ErrM.hs

Java backend:

• [ ] remove A arg from generated visitor, at least by option

Remove backends:

• [x] C# (is untested; Johan Broberg)
• [x] profiles (broken)
• [x] CNF (bad performance, see #270; licensed under GPL-2; JP Bernardy)

[andreasabel]

BNFC 2.9 will be dedicated to the license change to BSD-3-clause. Other breaking changes can be part of 2.10 or 3.0.