- 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 CRR demo code
- remove versioneye badge 😭

add TransmittableThreadLocal.Transmitter, expose internal capture/replay/restore operations for TTL values

1. Transmitter#capture: captures TTL values in current thread
2. Transmitter#replay: replays the captured TTL values after back up
the current ones
3. Transmitter#restore: restores current thread to state before replay

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

- update url of project repo
- update maven dependency repo
- update versioneye url and upgrade maven dependency version

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