- build by java 8 with java 6 source/target
    - full functions with java 8 support(ForkJoinPoolTest)
    - support java 6
- Travis ci has multiple java version: java 6/7/8/9
- scripts and test case/demo cleanup

- 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'