feat: Easy Termopen for Previewer (#88)

First pass, but seems to work. Fixed a few other related items, so pushing it to master now.

* [WIP]: Wed 16 Sep 2020 05:17:10 PM EDT

* [WIP]: Wed 16 Sep 2020 06:10:33 PM EDT

* [WIP]: Wed 16 Sep 2020 06:19:43 PM EDT

lua/telescope/from_entry.lua

@@ -0,0 +1,26 @@
+--[[ =============================================================================
+
+Get metadata from entries.
+
+This file is still WIP, so expect some changes if you're trying to consume these APIs.
+
+This will provide standard mechanism for accessing information from an entry.
+
+--============================================================================= ]]
+
+local from_entry = {}
+
+function from_entry.path(entry, validate)
+  local path = entry.path
+  if path == nil then path = entry.filename end
+  if path == nil then path = entry.value end
+  if path == nil then print("Invalid entry", vim.inspect(entry)); return end
+
+  if validate and not vim.fn.filereadable(path) then
+    return
+  end
+
+  return path
+end
+
+return from_entry