a_thread_pool 1.1.6

a isolate util, help developers use Isolate more friendly under the flutter framework to activate the multi-core performance of the device.

[1.1.6] - fix format [1.1.5] - fix add library define [1.1.4] - fix export types [1.1.0] - support delay [1.0.9] - adjust README [1.0.8] - update demo [1.0.3] - init