Added support for truncation.

Array entries, object properties and string length can be configured to
be truncated so the log output stays clean. Pay attention however: the
truncation may hide logging elements you don't want to miss.
Fixed array truncation

Corrected maxArrayKeys option to maxArrayLength. Arrays are now
truncated correctly.
Simplified object truncation

Truncation string is now append at the end of the object, without a key.
Fixed truncating to an ampty array

When trunctation results in an empty array the truncation String must
still be shown.
More elaborate option checking

Truncation should still work when truncated to 0. This was not handled
properly.
Surround with quotes after stringifying strings
Added tests for truncation

Several tests have been added to test scenarios for truncation of
Strings, Arrays and Objects.
Merge pull request #21 from mattijs/shortener

Added support for truncation of Strings, Arrays and Objects