feat(bookmarks): add bookmark feature

[kyazdani42]

Uses the signcolum to display the mark status.
Marks are saved in memory for now, we'll see if we want to implement a
filesystem save for the marks (would not be hard).
Added m keybinding to toggle the mark on the node
Users can call require "nvim-tree.marks".get_marks() which returns a
list of absolute paths.

superseeds #612

TODO:

• small bulk rename action (in followup PR)

Fixes #221
Fixes #51
Fixes #595
Fixes #509

[alex-courtis]

Users will complain when they see that marks do not yet do anything. Here's a branch that hides marks behind a "feature flag" feat/bookmarks...feat/bookmarks-amc

At some point can do more with the marks API e.g.
set_marks(table)
toggle_mark(string)
add_mark(string)
remove_mark(string)

In the far future we could define an official API e.g.
require "nvim-tree-api".toggle()
require "nvim-tree-api".get_marks()

[kyazdani42]

@alex-courtis i don't think hiding this behind a feature flag is useful, i think first leaving a simple api for the users so people can start building integration with the marks would be better. Even if people complain, they can just script something and open a PR if they feel the feature they write would be useful in nvim-tree.
I think we could add a note in the contributing.md for the marks, such as how to develop a feature for it. I think i also could add a bulk action method for removal, moving or such.

[alex-courtis]

@alex-courtis i don't think hiding this behind a feature flag is useful, i think first leaving a simple api for the users so people can start building integration with the marks would be better. Even if people complain, they can just script something and open a PR if they feel the feature they write would be useful in nvim-tree. I think we could add a note in the contributing.md for the marks, such as how to develop a feature for it. I think i also could add a bulk action method for removal, moving or such.

Sounds good. Feature flagging functionality is not nice and creates future work.

Having a useful API should be enough to keep people happy.

[alex-courtis]

NvimTreeBookmark in :help

[kyazdani42]

I've added the docs, lets merge this and add the features in followup PRs

[alex-courtis]

I've added the docs, lets merge this and add the features in followup PRs

Yes. Long running branches are undesirable.

I'll get to the follow up PRs on the weekend.