Parameterized sign in SQL queries.
Added a test case using <> operator.
Fixed style.
Merge pull request #549 from sophron/sql-non-equal-operator

Database API sign support
Remove contact in place (without rebuilding list).
Docstring fixes.
Just a list.
Honour import style.
Delegate removal to python. Avoid recreating list.

* Using list.remove means the element is removed
  in-place and no new list is created. This lessens
  the space requirements and may improve speed.
Simplify getContacts.
More docstring fixes.
Raise value error when removing non-existing contact.

Fix #535.
Enable due test.
Remove execute flag.
Wrap long line.