BREAKING CHANGE: Delta Pager + Large Refactor (#43)

BREAKING CHANGE: This MR addresses an underlying issue with the original implementation in regards to detecting line numbers for comments. 

As such, this is a major breaking change. The setup function signature has changed, please review the `README.md` for the new arguments. The delta pager has also been added as a dependency: https://github.com/dandavison/delta

There will be future work to implement a native solution for parsing changes and line numbers.

lua/gitlab/actions/assignees_and_reviewers.lua

@@ -0,0 +1,73 @@
+-- This module is responsible for the assignment of reviewers
+-- and assignees in Gitlab, those who must review an MR.
+local u           = require("gitlab.utils")
+local job         = require("gitlab.job")
+local state       = require("gitlab.state")
+local M           = {}
+
+M.add_assignee    = function()
+  M.add_popup('assignee')
+end
+
+M.delete_assignee = function()
+  M.delete_popup('assignee')
+end
+
+M.add_reviewer    = function()
+  M.add_popup('reviewer')
+end
+
+M.delete_reviewer = function()
+  M.delete_popup('reviewer')
+end
+
+M.add_popup       = function(type)
+  local plural = type .. 's'
+  local current = state.INFO[plural]
+  local eligible = M.filter_eligible(state.PROJECT_MEMBERS, current)
+  vim.ui.select(eligible, {
+    prompt = 'Choose ' .. type .. ' to add',
+    format_item = function(user)
+      return user.username .. " (" .. user.name .. ")"
+    end
+  }, function(choice)
+    if not choice then return end
+    local current_ids = u.extract(current, 'id')
+    table.insert(current_ids, choice.id)
+    local json = vim.json.encode({ ids = current_ids })
+    job.run_job("/mr/" .. type, "PUT", json, function(data)
+      vim.notify(data.message, vim.log.levels.INFO)
+      state.INFO[plural] = data[plural]
+    end)
+  end)
+end
+
+M.delete_popup    = function(type)
+  local plural = type .. 's'
+  local current = state.INFO[plural]
+  vim.ui.select(current, {
+    prompt = 'Choose ' .. type .. ' to delete',
+    format_item = function(user)
+      return user.username .. " (" .. user.name .. ")"
+    end
+  }, function(choice)
+    if not choice then return end
+    local ids = u.extract(M.filter_eligible(current, { choice }), 'id')
+    local json = vim.json.encode({ ids = ids })
+    job.run_job("/mr/" .. type, "PUT", json, function(data)
+      vim.notify(data.message, vim.log.levels.INFO)
+      state.INFO[plural] = data[plural]
+    end)
+  end)
+end
+
+M.filter_eligible = function(current, to_remove)
+  local ids = u.extract(to_remove, 'id')
+  local res = {}
+  for _, member in ipairs(current) do
+    if not u.contains(ids, member.id) then table.insert(res, member) end
+  end
+  return res
+end
+
+return M