Allow the LDAP configuration options to be fetched asynchronously

This is usefull for example if you want to reconfigure your application
without having to restart your node server.
Revert name change
Added couple of tests for options as function

Pull request #8 did not contain any tests. Add some that verify it works
now, and then get rid of regression caused by the pull request without
breaking desired functionality.
Minor changes to follow the conventions used
Providing a single function is no more an error

With the possibility to pass a function as options we cannot assume the
given parameter is a verify callback if it's a function, thus removed
the test.
Documentation changes
Added @MichaelBailly to contributors
Use bind/call instead of self = this

Finally changed to binding scope since the new pull request used binding
as well. Now the scope is handled the same way in all code.
Merge branch 'linagora-async-config'

Add possibility give a function as options to LDAP strategy.

Closes #8
Updated dependencies