add async request functions
Merge branch 'master' into async
use Random.Xor128
fix callback function
add function to run asynchronously and poll the results
some refactorings

- change variable's name and structure
  - s:actions -> s:async_works
  - dict -> list
- remove id and make works a simple queue
- check existence of exit_status
- add tag to know the kind of work
no plugin is allowed to have no test
callback of request returns the same output as synchronous version
fix variables' names
execute wandbox asynchronously
add indent to subsections
improve dumping result to message

using feedkeys() hack because popup output in autocmd is not allowed.
fix name of function

wandbox#_dump_results_for_autocmd_workaround() -> wandbox#_dump_compile_results_for_autocmd_workaround()
determine to execute synchronously or asynchronously automatically
can abort all asynchronous works

This remains temporary files which should be sweeped.
output result even if in insert mode
add foldings
remove useless code
execute list API asynchronously
change functions' name

bark() -> show_option_list()
bark_async() -> show_option_list_async()