add ResourceExistsPropertyDefiner
Introducing AbstractDiscriminator base class to avoid repeated start()/stop() implementation in each concrete Discriminator
Support attribute "optional" in include element

Support attribute "optional" in include element to prevent errors on
inclusion of non-existent files without requiring Janino and
FileExistsPropertyDefiner.
LOGBACK-835 - make timestamp properties default to local scope. Can be overriden by setting scope attribute
LOGBACK-833 - allow previously defined properties (in local scope) to be seen by SiftingJoranConfigurator
 * implemented part two of Ceki's suggestion
 * add getCopyOfPropertyMap() to the PropertyContainer and thus InterpretationContext
 * use local properties that are ineffect at time of creation of SiftingAppender to seed the properties map used when creting the child appenders and properties
 * removed some generics warnings
 * in AppenderFactoryBase use List.subList() rather than "copy whole array then delete and re-shuffle elements"
LOGBACK-835 - corrected status message in timestamp
LOGBACK-833 - unit test improvements to check that a local timestamp property really was set
LOGBACK-246 implemented
modify ThreadPoolExecutor as discussed in https://github.com/qos-ch/logback/commit/00abc35c
add or correct links to examples
added blurb about LOGBACK-749
added reference to logback-decoder project
native speaker requirement for the logback 10 minutes document
Merge pull request #111 from diroussel/LOGBACK-833-sift-variables

LOGBACK-833 Fixes for variables in sifting appender
property renamed
added test for property propagation in siftingAppender, minor variable name changes
removed ThreadPoolFactoryBean and related classes
added MockExecutorService to support unit tests
removed ThreadPoolFactoryBean from nested component rules
ServerSocketAppenderBase now uses context executor service