Improve parsing errors reporting

[pombredanne]

The exception messages returned from parse are often not really useful not meaningful. We should improve this. Also several TypeError exceptions are returned as is while parsing

[pombredanne]

Another parsing error: with this expression this () that, parsing will get this:

in test_parse_errors
    licensing.parse('with ( )this')
  File "/test.py", line 246, in parse
    expression = algebra.parse(expression, simplify)
  File "/boolean/boolean.py", line 227, in parse
    ast[0].append(ast[2])
IndexError: list index out of range