replace synchronize on snippet initialization by ReentrantReadWriteLock
for better performance.
remove the parse method in ElementUtil because it is not being used at
anywhere and it is also likely to be used wrongly.
add a common servlet for common purpose
allow configure url rule extractor
add binary data writer
add generic file handler(include binary file handlering)
refactory dispatcher api definition
allow output a warning message when a certain selector does not refer to
any existing element.