- updated a few classes' addError calls to display a link to the codes.html page

and verifies that the context and mdc values are passed and are readable
once the event has been deserialized.

- quick intro about PatternLayout and pattern conversion
- explanation of format modifier on classnames, with examples
- doc in progress 

required for ibiblio bundling

- updated test so that it does not tests serialization but only appender behaviour.

- added IThrowableRenderer, an interface to allow multiple implementations of ThrowableRenderer to be easily used
- added NOPThrowableRenderer, a no op implementation of the IThrowableRenderer interface
- the HTMLLayout now uses the DefaultThrowableRenderer by default.
- updated tests
- on going work on the HTMLLayout javadoc

The ThrowableRenderer can be specified in the configuration file. If it is present, it is used to render the Exception in a new line. If no ThrowableRenderer is specified, the user must add a %ex to the pattern used by the HTMLLayout to display Exceptions.

- corrected docType declaration
- suppressed two unused variables

- updated HTMLLayout to use the new class
- updated tests
- removed the unnecessary method onNewLine from ThrowableHandlingConverter

- slf4j-api 1.1.0-beta0 is now a logback-classic dependency
 
consequently, several classes which were both in lb-classic and slf4j-api 
were removed (from classic).

- getLogger method was removed from LoggerContextAware (we no longer need loggers
 to report internal errors as we use Status instead)
  DateConverter and ClassicConverter were modified as a consequence to use Status instead
 of logger

- added test class

- modified SMTPAppender accordingly
- updated tests
- updated pom.xml files

or builds the link to a user-specified external css file.
- updated test

- updated html code to xhtml
- improved test

- defaultConverterMap in PatternLayout now is public, to allow sharing of the map with HTMLLayout
- added a Dom4j dependency for Classic tests, in pom.xml
- a few re-format of classes, replacing tabs by spaces

minor update

- added mdc keyword in PatternLayout

- updated PatternLayout accordingly