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

This reverts commit ada90204.
only access key, no need use entrySet #87

Improve performance, more info see Alibaba Java Coding Guidelines
Item 12 of Collection section

Merge pull request #87 from lispking/master

- lock maven version, not dependent for system install
- simpilfy appveyor ci, no need maven install manually

use version 3.2.5 so as to support java 6

see travis-ci/travis-ci#7884

- shorten sleep time for speedup test

add test case for ThreadPoolExecutor#remove in AgentCheck