fix: Reduce memory leaks (#148)

It is not 100% clear that we've gotten ALL the memory leaks, but it
seems much much much better and doesn't look like it's going to die
immediately or as often anymore :)

lua/telescope/_compat.lua

@@ -0,0 +1,71 @@
+
+vim.deepcopy = (function()
+  local function _id(v)
+    return v
+  end
+
+  local deepcopy_funcs = {
+    table = function(orig)
+      local copy = {}
+
+      if vim._empty_dict_mt ~= nil and getmetatable(orig) == vim._empty_dict_mt then
+        copy = vim.empty_dict()
+      end
+
+      for k, v in pairs(orig) do
+        copy[vim.deepcopy(k)] = vim.deepcopy(v)
+      end
+
+      if getmetatable(orig) then
+        setmetatable(copy, getmetatable(orig))
+      end
+
+      return copy
+    end,
+    ['function'] = _id or function(orig)
+      local ok, dumped = pcall(string.dump, orig)
+      if not ok then
+        error(debug.traceback(dumped))
+      end
+
+      local cloned = loadstring(dumped)
+      local i = 1
+      while true do
+        local name = debug.getupvalue(orig, i)
+        if not name then
+          break
+        end
+        debug.upvaluejoin(cloned, i, orig, i)
+        i = i + 1
+      end
+      return cloned
+    end,
+    number = _id,
+    string = _id,
+    ['nil'] = _id,
+    boolean = _id,
+  }
+
+  return function(orig)
+    local f = deepcopy_funcs[type(orig)]
+    if f then
+      return f(orig)
+    else
+      error("Cannot deepcopy object of type "..type(orig))
+    end
+  end
+end)()
+
+
+
+table.clear = table.clear or function(t)
+  for k in pairs (t) do
+      t[k] = nil
+  end
+end
+
+table.pop = table.pop or function(t, k)
+  local val = t[k]
+  t[k] = nil
+  return val
+end