Rewriting N3 lexer: Support for formulas

The lexer has been rewritten such that it better corresponds to the
grammar at
  http://www.w3.org/2000/10/swap/grammar/n3-ietf.txt
Note that this grammar is not fully correct in my opinion. For example
a dot may introduce a pathtail, for example in ':something.log:uri',
but the grammar only allows pathtails with ! or ^.

New features:
- Formulas in curly braces { }
- quick variables (starting with ?)
- quantifiers @forSome, @forAll
- numbers and booleans
- =>, =, <=
- property paths with '.', '^', '!', for example ':something.log:uri'
Merge pull request #2 from uholzer/n3revision

N3 lexer: support for formulas and more