Release v0.19

[0.19] 2020-06-28

Added

• Add clap#run(provider) which is similar to fzf#run(). The argument provider is a Dict like g:clap_provider_foo with an optional extra field specifying the provider id. It can used for adhoc running, don't use it with a source that probably has a fair mount of items as it's normally undeveloped in performance. #433
• Impl async preview for git_files and history provider.

Improved

• Make the indicator winwidth a bit adpative when using the relative layout.
• Ensure the sign always visiable when running maple via job.

Fixed

• Fixed the win contexted execute() for jumps and marks provider when clap window is not yet visible.