Utility classes should not have public constructors

- update fuction description of README
- add toc of README
- link to javadoc 7 instead of javadoc 6

- update code and doc: concept multi-thread context(MTC) => TTL
- package mtc => ttl
- update word 'context' to 'TTL value'

add jdk agent, transform class java.util.concurrent.ThreadPoolExecutor and  java.util.concurrent.ScheduledThreadPoolExecutor