add support for cmake find_package

[poor-circle]

Why

Add support for cmake find_package. User can import async_simple easily.

Some package managers also use it. we can add async_simple to package manager later.

Example

find_package(async_simple REQUIRED)
target_link_libraries(<your-target-name> PRIVATE async_simple::async_simple) # dynamic_link
                                 # async_simple::async_simple_header_only   
                                 # async_simple::async_simple_static  

[ChuanqiXu9]

Windows CI is failing. Please take a look.

[poor-circle]

Windows CI is failing. Please take a look.

Fixed.