denite.nvim source for key mappings. (Partial) port of the mapping source of unite.vim.
I used to use the feature in unite.vim only for searching.
So I ported only the searching feature: the denite-mappoing source provides no actions so far.
In the future, I might add a feature to open the line where the mapping is defined.
It would be implemented with :verbose map command and the line kind of denite.nvim.